Are you mobile? the best alternative is prob the clients bed or dining table if they have one of those huge sturdy ones (prob best option). ensure you cover it, preferably with a large sheet then couch roll. if doing it on a bed you may want to kneel down, as you may come away with a really bad back ache if waxing for too long.
I have heard of some people doing it on the floor, but this imo is the most awkward, as you dont have the same field of vision down there, and is'nt v professional or comforable (for you esp).