So, here's the thing. All third party N64 controllers (that I know of) use pots. The first party controllers use what they call a "Transistor Slotted Interrupter" for each axis. They're identical to what PC mice use. Anyway, that's not important now. The point is, you HAVE to use a third party controller.So, time for pictures. Oh, and sorry for the blur... I realized my camera lens had a smudge on it after I took all the pictures... plus the lighting in the room I was in wasn't too great.
First, a picture of the completed mod:
I used hot glue, because it's simple, it's strong and this mod is temporary. I had to mount the board/joystick on the outside of the controller because I couldn't fit it inside without some dremeling, and again, it's temporary. As a result, it's a little too far raised, and it doesn't have the plastic on the outside with the 8 "notches" that the joystick snaps to. So, it feels more like a PSX joystick than a Gamecube joystick in that respect. But it's still 100% better than any N64 joystick I've used. And no... I didn't bother to do anything fancy with the wires. They just kinda snake off into the bottom side of the controller, where I made a small hole with a pair of pliers.
This picture shows the bottom of each joystick. From left to right, a Gamecube joystick, a Gamecube C-joystick and a PSX joystick. As you can see, they all use the same size/type of hole to slip onto the base, so you can use any of them by simply slipping them on. The only difference is that the PSX joystick doesn't have that small notch in it that the Gamecube joysticks have. This doesn't matter, though. It will still fit fine. Nintendo only put those notches there for orientation.
This is what the joystick base looks like without an actual joystick on it.
This is what it looks like with a Gamecube joystick on it... well, sorta... that's the destroyed one without the rubber grip. I recommend using this joystick if you can. It feels MUCH better than the C-joystick, IMO.
And this is what it looks like with a PSX joystick on it. I prefer this joystick the least... with the C-joystick in the middle.
And now, some gut pics:
I left the old joystick "box" in the controller and just took the actual stick out so that the C-joystick board had something to rest on instead of it being hollow under the board.
...But that's what it looks like without the old joystick box. What you see directly below the yellow and green thing (PCB and rubber contact for the Z button) is the bottom of the C-joystick board.
What you should be looking at here are the two white things in the center of the picture. The one on the right with the four white wires attached to it is the connector for the C-joystick. The other end of the wires are soldered directly to the C-joystick board. The connector on the left with black wires attached to it was salvaged off an old serial mouse I had collecting dust. Yes, it is a 5-pin connector, and the C-joystick connector has for pins, but it still plugs in fine. I just don't use the fifth pin. Besides, it was between that, and soldering wires directly to the joystick board... which probably would have required me to remove the other wires, too. I didn't want to do that, because as I said before, this is temporary. So, the connector is optional, obviously. The black wires are soldered to the other colored wires that I ripped off from the old joystick. Why didn't I just solder the colored wires to the connector instead of just extending them and making more work for myself by adding the black wires? I... honestly have no idea. :laugh:
This is the schematic of the C-joystick, reverse-engineered by yours truly. It wasn't easy, either. The board has a silk-screen over the whole thing, making it hard to see the traces. I actually had to use my multimeter to tell me almost everything... I couldn't just follow the traces. The 1 and the 4 are both silk-screened on the board, where the wires are soldered. Pin one of the connector in the schematic is VCC, the square box. One important thing to remember about all schematics, is that when there's a one square contact on a multi-contact part and the rest on the contacts are circles, the square one is always pin 1.
I probably left some details out that I meant to include, but I think this is enough information for just about anyone to pull of this mod. I've only tested this with a "SuperPad 64" controller by performance, but it will probably work with any third party controller. It all depends on the resistance of the pots they use, but I don't think they're very picky. One last thing to remember, is that the pots used inside third party controllers are usually wired with ground on one side and VCC on the other side. The middle contact is wired to the chip. To figure out which side is VCC and which side is ground, try to follow the traces from the spot where the wires for the joystick are soldered onto the board, and see which one leads to a spot that you know is ground. Or, you can test it with a multimeter. If it's wired in reverse, the axis's will be reversed. Left will be right, right will be left, up will be down, and down will be up. I could explain the reasoning for this, but it's really not important enough to go through right now.
Anyway, I'm gonna go setup my soldering iron and try something else I just thought of.
Hope you guys find this information helpful, as it took me all day to write up. Feel free to ask me any questions you might still have. Just make sure you read this whole thing before asking. 
Oh, also, I'm not checking this for typos like I normally would. :laugh:
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So, it's pretty durable, and works well enough for me to blow through all the levels that quickly. I didn't even play it for more than a few hours each day, either. 
'Course... that's not as cool as this: 
Signing up is very easy, though. You don't even have to sign into your email for an activation link or anything. Once you sign up it brings you straight to the video... you don't even have to sign in either. Trust me, it's very, very worth it. 