The way I understand it is that the DS doesn't have the necessary chip for GBC compatibility, they left it out to save cost. The only reason it plays GBA games (from the articles I've read) is because one of the chips the DS uses is the same as the main processor of the GBA or something like that, so they included GBA compatibility as a great selling point that wouldn't cost them much.
Adding PCE console specific layer on top of that, makes for an interesting challenge (no, not a reference to Ys II).
You can heat up the tip of a ball point pen (without the ink cartridge in it, of course) then press it over the screw heads until it hardens, that worked for me way back before I knew you could buy them on ebay.