Well luck happen, this is subject that we have touched upon before I believe, there are many suggestions, how ever not knowing you or your wife I would have to say if she is a partner who likes to try new things say in your sex life she will probably be ok with it, another way that worked for a friend of mine is if you have a smart phone or tablet you can get an app. that is a foreplay game that you can customize to your liking and as one the items you can customize is to have your partner swap underwear, or you could play a game of sexual truth or dare and make it a dare to swap underware.
I hope this helps I think you get a lot of ideas here.
