Technically, yeah. But to be honest, it wouldn't work very well. And no-one would really bother doing it. I'm not sure how simple or difficult it is though, it might be just a simple "assign motion-sensing to a certain control on the gba", or it might be almost impossible, as the commands built into the ROM are probably incredibly complicated when it comes down to motion-sensing (physics-based). Also, I don't know many cases of DS hacking being done outside of translation and patches, so this would mean a further step into the DS' coding.
Just don't think it's worth the trouble.