If they head towards that position between my legs, I will reach down and stroke their cock so that I have control over it.
If I come up for a kiss after oral, I will straddle one of their legs. I had a guy repeatedly try to get both legs inside of mine and as soon as he got the chance he rubbed against me. I scolded him harshly and he didn't seem put out. Just a vague thing about only wanting to rub it. I didn't throw him out but I was distinctly colder for the remaining few minutes of the booking. After he'd cum he'd tried to chat about music and I reminded him that I was not impressed and left him to get dressed in silence.
I probably should have just ended the booking but avoiding a scene is also a priority.