Yes, I'd say most girls who provide it at amps will initiate it during the ass teasing portion of the massage - as the sooner above mentioned, just arch your back or tell her you like it. Same goes for rimming from the front, most sps will get the point if you start raising your hips / hole towards her mouth , especially during bls. A gentle push on the head downwards helps also or simply just ask - you'll be suprised how many sps offer it but simply don't advertise it often due to personal preference and hygiene etc.