If you have the cash, just use items to raise their EVs (Protien, Carbos, Etc), so they still get them when you use the rare candy on them.
As much as I know about the game, I only know about the Darkrai and Sheimi glitch (which the Elite 4 skipping glitch is a part of), I know nothing about cloning items.
The drugs only raise the EVs so far though, after a point they dont work and you need to do the battle thing to fill up the rest. There's a guide somewhere on it but… I'm feeling lazy XD
Edit: Meh, i got a little less lazy... http://www.gamefaqs.com/portable/gbadvance/file/921905/36819