Okay, here's my solution, but it may take a while to go into action.
1: Find someone who has a crush on your current girlfriend - for bonuses, make sure he's at least attractive, and he's your friend.
2: Introduce the duo and make them get to know each other. If there's chemistry visible, that's excellent. If there's not, it may show up later - one of them, maybe both are probably too nervous to admit. If it doesn't show up later, refer to solution #2.
3: After around 3-5 "get-togethers" where there is only you, your girlfriend and your friend hanging out, preferably in private, get one of them to invite the other to a special dinner - one that you won't be included in.
4: By this point, if the other one accepted the invitation, that's excellent. In only a matter of days, your girlfriend will probably break up with you for your friend, but you'll both be happy.
Then you can wait a bit (note the "jump/jump/dump" cycle someone posted above - you do NOT want that image appearing to your new girlfriend), then ask out your friend you liked.
Hope this works. Good luck.
