I am a provider who offers several fetish scenes and this as kinda been an obsticule in the past. When asking a provider, ask when setting up the meeting. You want to know that she really can do what you wanting. Asking over the phone can be someone what simple. I can't speak for every provider, But I know that I have heard EVERYTHING!! So, nothing you say is going to make me say "OMG are you crazy?!?". Just ask do you offer such and such fetishes? She will either say yes or no. I have had men schedule an appt before leading me to believe that it was a GFE session, so I was prepare for that, when he showed up he tells me that he wants a Dominatrix scene. Well now I am scrambling to get that stuff ready and get in that "bitchy" frame of mine (cause its doesn't come natural). So in turn he probably didn't get my best by springing it on me.
When talking to a gf or wife, I agree with funny boy, the way to go is a "dream". IE: "Honey I had the craziest dream last night: You were naked hanging from the ceiling fan with a flashlight in your tooshie" LMAO
Or whatever your fantasy is. Gauge her reaction. Read her body language and voice tone. And if she seems to be liking it, say would you ever do something like that? and Go from there. I can understand this part. I have some socially taboo fetishes that I love, but can be hard to tell someone. But its worth it if you do .
as far as telling a provider, We have heard alot, and we are here to please you. TO make your fantasies come true (if we can). So, don't be shy, hint: look for those who advertise fetishes.
Good luck!
How do you ask if you can...
so maybe I should just stick to replies. 
