Idk, IMO even with you suggesting it for fun, it could still be something you use for pleasure later. It's not right to trick someone into a fetish without being upfront about the purpose.
You need to tell them upfront and what the purpose is. If they're into it, they're into it. If they say no, they say no.
If you're worried they'll say no if you reveal the true intent, you probably shouldn't be asking in the first place.
Maybe a bad choice of words but I don't think you should try and "convince" someone to do this.
If you just tell them, and present it in a way that is not creepy, genuine and appeals to them, then they'll want to participate. Make sure you are clear on your intentions however, honesty is the best policy in my opinion.
As an outsider looking in, my boyfriend straight up told me about it and was honest with me (before we were even together) but to me I don't think it's right if it has the same effect on you, if it's still getting you off and turning you on, even if they don't know about it, kinda taints the waters if you know what I mean? These are just my thoughts, I don't judge anyone or hold it against them. I know my boyfriend tries to stay away from that even if someone else wants to do that? Like they want to make a bet with him and the loser gets a pie, unless they know about his fetish he won't do that to the "innocent". There's enough free out there online than to take advantage of someone who later if they were to find out about that, probably wouldn't be to happy. Just my few cents.
Well, if Regis were still here posting, he'd probably say "with chloroform, duct tape, and a handful of zip ties."
That said, I'd go with the other posters here and just come right out and tell that person "this is what turns me on; this is who I am and I love it and if you're down to try it out, that'd be a huge turn-on for me." Or however you might phrase it.
I agree with what other people have already said. Just to look at this from another perspective, I'm sure there are various activities that you've never done. How would someone persuade you to try them out? I think it depends on why you've never done them.
Here are a few hypothetical examples; obviously the specifics will vary from person to person.
Friend: "Hey, it's Dave's stag night, so we're all going kite surfing on the beach. Do you want to come along?" You: "Yeah, sure. I wouldn't go out of my way for something like that, but if you're organising it then I'm happy to give it a go."
Friend: "Let's all go bungee jumping!" You: "Um, I'm not sure about that." Friend: "Honestly, you should. I was really nervous the first time I did it, but afterwards I found it a real confidence boost: if I could get through that, I could get through my presentations at work." You: "Ok, let's give it a go." (The key point here is that the friend is being sincere and enthusiastic about why they enjoy this activity. I'm not suggesting that WAM would inherently be good for self-esteem.)
Friend: "Hey, did you watch "I'm a celebrity, get me out of here" last night? I'll give you 5 quid if you stick your head in this hole and let a tarantula crawl over your face." You: "Nope, nope, nope. There's not enough money in the world to make me do that!" (This might not just be based on fear. E.g. if you went to the fairground and there were people getting their faces painted like lions and tigers, you might say "Nope, not for me, I'd feel stupid.")
So, if someone views WAM in category 3, there's no point even suggesting it. If they view it in category 1, they won't need much persuading. If it's category 2, you need to be upfront about why you're suggesting it, which comes back to what other people said.