As far as I know it cannot be done. Not in TS2, not in SLS. I think there was some sort of hack or method for doing it in TS2 but I don't think anyone ever came up with a truly safe method of doing it. From memory, it involved editing stuff with SimPE, so it was not an easy fix, either.
ETA: Apparently you have to get a SimPE plug-in
and then it will remove all the outfits from the wardrobe so the sim has to re-buy everything.