Skip the knife, but put rubbing alcohol on your hand every time you decide to let the fap fly...if it doesn't burn, you're not doing it too often, but when it starts to burn, you'll have a built-in warning signal that will take the fun out of it, unless your kink is also BDSM.
Then do like the last guy said and go work out. Squeeze a tennis ball though, so your brain gets the sensory input from your hand that's a lot like what it would get from Rosie.
Jesus Christ who hurt you