making holes in jeans?

[cut-opentragedy.livejournal.com]

i am trying to make a big hole in the knee area on a pair of jeans, but i've never done this before so i don't know how to do it. obviously, i can just cut a hole, but i don't think i'd get the look i want.
after i make the hole, i want the white thread that goes across to still be there... like so.


i want the rip to be wider than the ones in the picture, but still kind of.... stringy, i guess.
any help would be great.
thanks