Cut the bottom/center out so it's more like a skirt, then cut a bunch of vertical cuts from the bottom to halfway up. This isn't a picture of boxers but to give you an idea of what I'm thinking:
https://www.milly.com/cdn/shop/produ...ACK_1_485x.jpg
Then wear them as PJs for the next week.
I don't want to destroy any of my womens' underwear, but I'll destroy a couple pairs of me mens' underwear - I have breifs and boxer breifs.