There's no reason you can't cut it into 8 pieces, but I don't know of an easy way to do it. I use a pill splitter to get 4 pieces, and it's hard enough as it is to get them equal size.
It might be easier if you have the round pills instead of the oblong ones I get. One possibility is to cut into quarters using the splitter, then use a sharp blade to cut each piece in half. (Just try to make clean cuts so not too much of the drug turns to powder.)