if you've been going to the same guy for several visits, there should be trust established by now for you to, politely, simply ask if he offers sensual or erotic options, as RandyVue suggests above.....
otherwise, your body language might (??) lead to something......about a third thru the session, while still on your stomach and well before you turn over, try spreading your legs a bit farther apart.......also, some light moans and "oh, that feels good" utterances may suggest something to him......also, ask if he'd be comfortable doing the massage naked, if he isn't doing it already that way......
as always, be polite and professional.....never associate money with any "acts"......