I've found a way to get EVEN MORE out of your intensive RAD´sing!
When you have gotten to a wheelie where the back scrapes the ground, let go of the gas just a little, so that the back stops scraping (keep tapping forward), and hit the gas again. If timed right, you will be in a wheelie which will not go down. So now you get the effect of a usual RAD´s but without the friction from the back scraping.
Have fun reaching higher heights