I think that would be too random depending on your fluid intake. It may not be good for your bladder either.
A regular consistant practice with a kegel/reverse kegel routine outside of sex will best give you a well balanced pelvic floor. Read up on them here and find a routine that gives you a good balance over time. If you have pre-ejac then more reverse kegels are usually effective in helping maintain arousal control and keeping you in the parasympathetic state.