I do OWO (at my discretion) but not CIM, and I've only had one client push it - he did the head grabbing thing but I was lucky/quick and pulled away just before he came, so it turned into COB.
If there's pre-cum I wipe it away with my hand or a wetwipe.
Have you done CIM with a partner? I did a couple of times with one, who was very clean-living, and it was fine. But then with someone else, who was a smoker and probably didn't have a great diet, it was so rank I couldn't get rid of the taste for 48h and it put me off for life! I ask as if you're OK with it, there's definitely a market for 'blow and go' quickies (which I don't do).