You really don't want to coerce or trick your wife into something that she isn't comfortable doing. Unless your marriage isn't important.
Explain to her why you want it. She may feel threatened that once she does it, then you'll want to do it with other woman. Set the ground rules and let her know it will only be her indulging, or both of you, etc. She may be afraid your gay, etc. Communicate!
you could always tell her you had sex with her best friend/sister/mother/father that may make her want to get back at you and do it as well.
You need to treasure your wife more and stop wanting another man to touch her. Your making a big mistake.
good answer from biondetta
No trick this is not a magical
Act... Will only happen if she is agreeable to being shared. Good luck though!!
tell her to think of the other guy as a sex toy that you both are using for pleasure. He really is not a lover. he ismore of a prop for you to use for your sexual fantasy.