I've heard -- but not confirmed -- that such services are available at a certain location on 2nd Street in Manchester. (I'm not certain how discreet I'm supposed to be here, but if you were to wander over to the Back Pages of the internet and check in the NH section for a phone number ending in 5118, you might strike gold.)

On the other hand, I can speak from authority that the reviews for "Susan/Shallin" (see link) is actually an agency, with a rotating staff of masseuses of varying skills, and FS is pretty much always on the menu. I've been disappointed once or twice, but satisfied most of the time.