I have a regular like this. I've seen him several times so he's pretty comfortable with me and knows I'm not judgmental, so when he starts to feel too excited we have a code word and we just stop what we're doing and sit and talk for a bit, when he's ready to start up again he'll initiate it. I'll try to stretch out the time by doing things like kissing his neck/mouth/nipples, massages, running my hands through his hair, etc as opposed to hand jobs/OWO/RO etc as that gets him off too quickly.
I find the code word is less embarassing for him than having to say "I'm gonna come in my pants we need to stop." I just have to be super careful and go very slowly. The first time I saw him he came in his pants before I even got undressed and was so humiliated, but I didn't make a big deal about it and I think that made him comfortable enough to come back.
The good thing is I don't think many escorts would put up with all that and he knows it so I can not only count on him as a dependable regular but as a client who always leaves a great tip, which is pretty rare.