I know about that. Seen this?**There's a device called the Passme, you connect it between the DS cart slot and the DS game, you then load your homebrew game onto a GBA flash cart, and plug it into the GBA port. The passme, tells the DS theres a DS cart in, instead of a GBA cart, allowing the game on the GBA flash cart to be played like a DS games, with all the buttons, both screens, etc.
http://www.themodgods.com/2005/04/big-o ... hrough.htm