I wouldn't pull him if she's bucking him off, surprisingly every time I've seen this behavior it has ended up in a lock

Learning to palpate alleviates some of the anxiety about not knowing how far along they are.
I use a table leg and let them grab the leg and when they pull you pull your finger tips along the belly pushing up to feel for lumps.
The trick is to get her to relax her belly muscles while your pushing your finger tips into her belly to feel those lumps. Do be careful to not push too hard, many time it takes two or three pulls before getting the female to relax her belly.
I can usually feel the follicles when they are about marble size well before the snake ovulates.

I offer the female food until she ovulates, she may not take it but then again she might and if you don't offer it you won't know.