You might have got away with using one of the DSSlot to GBA slot file transfer deals and physically swapping a card but both of those need to be DLDI capable and the 3 in 1 is not.
Anyhow via wifi, not really: the DS to DS protocols have not been reverse engineered/implemented. You could do something with this though: http://forum.gbadev.org/viewtopic.php?t=11...0&postorder=asc
Failing that you could mess around with FTP.