Continue to stroke, and think back to just a few minutes ago when you were soft. During the next several hours for you, it'll be just a distant memory. What I am going to do to you will ensure your dick stays nice and hard after you leave me. Don't be worried though, because as I promised you will get more relief than a ruined orgasm as I am a girl of my word, but only if you've proved to me that you've earned it.
Earning it will take a lot. To start with, it will take doing what I say... beginning now. Fetch me a small glass, boy, and stroke while you're getting it so I have some eye candy to look at while I wait. Oh, and fill it with half with ice and up to the brim with water, and make sure you don't spill. Now run along, slave.