I don't mean to hijack the thread, but since neither of you specified who you were asking I guess it's not taboo for me to answer?
I don't think you can "open her mind to the possibility", she has to do that on her own. Simply plant the seed, and if she wants it to, it will grow. I put off confessing my interest in the lifestyle to my wife for a long time, thinking she would view it as perverted, ect. Turns out that I just sort of blurted it out one night during a discussion regarding several of our friends that had gotten divorces due to cheating. I told her that our relationship was more important to me than sex, that she was my best friend, and that if she ever felt the desire to have sex with someone else to simply be honest and tell me. Not only was it ok with me so long as she followed a few simple rules (condoms, discretion, honesty), but I actually found the thought of it rather arousing. I then sat back and waited for her to unload on me for even suggesting such a thing, instead she said that she herself had been thinking it might be hot to have a 3some with another girl, but she wasn't particularly interested in other guys. The conversation ended up with MY jaw on my chest, instead of the other way around like I thought it would, LOL. I had absolutely NO idea that she was the least bit bi curious, but she had just admitted it to me, and I was absolutely floored . . . and a bit turned on too I have to admit.
The 3some with myself and another guy just sort of happened however. Through our lifestyle involvement we found ourselves in a situation where it COULD happen, and it did. Had we tried to plan it, it probably never would've since she had stressed from the beginning that she wasn't particularly interested in other men. Even though it happened, and we both enjoyed it, it's still something that she's not interested in "planning". If it happens again she's all for it, but she's still not interested in trying to "make" it happen if that makes any sense at all.
The one thing that I CAN say with some assurance however, is that if your relationship situation is not one where you and your spouse can openly discuss such things, then swinging is probably not for you, at least not at this time. Sometimes the only way you can find out if you have the type of communication necessary is to try it, like I did. You might be pleased with the results, but then again you might not so proceed with caution. We had no idea that we could be so open with each other until we crossed that barrier, but it's been the best thing to hit our relationship in years since we did. Had she not been interested in the least however, I would've dropped the subject like a hot rock. Turns out that she had been thinking some of the same things that I had, and damn that's a beautiful thing when it happens.