Using a DS Flashcart as AR for GBA games.

Yes, the idea sounds crazy and I haven't found anything on the matter. However, think about it. On Pokémon D/P/Plat you could connect your game card to a S/R/E cartridge simply by inserting them in their respective places. Then, they'd interact. Ok, now this means that both slots must be connected somehow and that the information exchange is possible between them. Maybe there's already one, so I don't lose anything if I ask; is there any homebrew application that would let you use a Nintendo DS Flashcart as AR/ Gameshark for GBA games?

I don't know much about coding and all this stuff, so maybe this is utterly impossible.