You see, this is where being a Domme comes in useful... for a male sub what happens to his cum is his problem and usually *he* has to swallow it
After you have tried the cornstarch as a cum replacement,
try filling a swimming pool with it and walking on it. Non Newtonian fluids (which are actually a suspension, not a fluid) will allow you to walk on it so long as you don't stand still for too long (otherwise you sink...). Its been done before on TV with custard...
Have you ever tried licking it off him after you have had sex? Does that cause the same feelings?