It's not for the reason you may be thinking, though. While padding is usually done for enhancement purposes, Harris' double-density briefs were actually to prevent a Janet Jackson-esque wardrobe malfunction.
In a post-Oscars interview on Live! with Kelly & Michael, Harris reveals that they ran into some snags during dress rehearsal:
So we did the dress rehearsal, and I just had the pair of regular underwear on. But the lights! They see through things! So the Academy or the network or someone said we had to do something so you couldn’t tell my religion, so what they did was they had to take a second pair and sew it to the first to make it so that you couldn’t sort of see through it.
See, this is why you let the gays pick out their own underwear. We're masters at choosing just the right banana hammock to reveal or conceal the size, number, and religion of budgies we want you to know we're smuggling.
You can watch Harris' interview AFTER THE JUMP...