Offer to pay her big bucks
Okay.... First have you asked her if this is something that she would be interested in trying? If not you might want to start there. If you have and she has said that she is not interested, then I am sorry to say you are out of luck...... enjoy what you have with her.
Neither your wife will say yes or no, you have to tell her so she can be prepared about your fantasy, maybe you can open up the topic after you had sex and see her reaction.
You can alibi by telling your wife that you want to have a home service body massage. Let her have the body massage first. The third party need to pretend that this is a home service at first. She have to arouse her, and the rest is for you to move.
Well first you need to talk to her. Ask her if it's something she would be interested in, and then go from there. There isn't one magical thing to say that will make her want to. you can't force people to do something they don't want to do.
Bribe her: Brand new car, $10000 shopping gift voucher and be her slave for the next 50 years should work^^and yeah alcohol might help too. good luck
Well, have her do 3 lines of coke and then introduce her to this woman you want her to experiement with. Or take her to the science lab at the local university and see if a lab assistant with experiement with her. LOLOLOLOLOL
Show her some **** and ask her if she likes it... Be prepared to either get slapped or happy.