Do you mean having one enemy drop more than one type of item, or 1-2 (or more) of the same item? If it's the first, about the only way I could really think to do it would be having two of the same monster, though with separate treasure. Though if you wanted to do the 'common' and 'rare' item drops, that I'm not entirely certain how to pull off : /
If you're saying more of the latter, and want a goblin to drop one or two potions instead of the mandatory one, I'm sure it can be done, but it'll take a little bit of a script change, is all. I tried to do some of it on my own and I could get it to where they /always/ drop two, but I don't think I'm using the random function correctly