If you only want one player you don't need to bother mounting external controller ports. If you do want a second player, you could use small single plug connectors (3 male, 3 female needed) to connect a controller to the portable; that would make the connectors far smaller and give the same result.
You could even use regular stereo audio plugs (like on headphones). They have 3 contacts and are quite tiny - also, this keeps the controller in one plug. I'm thinking of doing this in mine, but I may not.
Current projects:
Ultimate N64 Guide
N64 Portable (x2)
NES Portable
Yup, same principle, except make the power (red line) the last one to connect (at the back of the jack) so you don't fry your system by giving it 3v across the negative or data line!
