Just another option for you ... you could always ask an FBSM provider to do the same thing, although you'd probably need to see her at least once to establish some trust, rather than coming up with "can I just worship your breasts" the first time.  The advantage to this is that, as a GENERAL RULE, I've found FBSM providers far more sensual than BDSM providers, so if the sensuality part is important to you, it's a good way to go.  When the sensual part is most important to me, I've found that "worship" with an FBSM provider is far more satisfying.
   

    One of the nice things about domination providers is, contrary to every other area of the sex industry, they tend to encourage direct (but polite and respectful) discussion of wants/needs/limits.  You're probably being cautious because any explicit talk with an FBSM provider is a huge no-no.  Not so with domination providers.  I would basically say something like, "I have one big fetish, and it is super-sensual breast worship.  You're the first mistress I've ever seen, and I'm a little worried about getting smacked and beaten up and then sent home to finish myself off, so may I ask if you're comfortable with a 100% sensual breast worship session?"

Keep in mind, if you're going with a domination provider, you almost certainly will be jerking yourself off in the studio, rather than getting a happy ending (unless reviews indicate otherwise).  Another reason to try the reverse route -- a worship session with an FBSM provider -- if the sensuality/sexuality is important to you.