I think the idea of positive reinforcement is not a bad idea at all, it is just something you have to have in your control. When you mention masturbating -- if you don't masturbate for a long enough time, you will have a wet dream. So it's not 100% in your control. Also, the human sex drive is very strong.
I worked with something a little easier, just to improve my dream recall. I gave up sweets and desserts, and I *only* ate a small candy immediately after remembering a dream. My brain caught on quickly. In fact, while still sucking on a candy, and falling back asleep, the flavor of the candy in my mouth will bring back memories of the previous dream. But I am extremely disciplined about this. If I don't remember a dream -- no candy.
This works well for me, as I live alone and cook my own meals, and buy my own food.