Quick question, are you happy with the way everything is set up at the moment from a handling point of view? If you are, then i'd suggest using the next to useless back brake to it's full advantage here and give it a dab to settle the back before it starts wagging as it is a way of altering and slowing the weight transfer bias without touching the suspension set up.
If you think about the rebound, the spring at full extension is relieving weight from the rear of the bike to its preload setting. So if the spring rebounds too quickly, then the force of the spring moving back to full extension is actually shifting the "weight" vertically. Combine this with the front diving and your body position, and the weight transfer moves to the front and lifts the rear. This is compounded by the rebound setting as it provides a force to "lift" as it fully extends. Draw it out on a piece of paper with arrows in the direction of the forces in action and it becomes more obvious to see.
If you aren't happy with the suspension set up, then search for a thread by DaveRSV I think it was which has a good link as to how to go about setting up sag and static sag. Without these in place first, you are unlikely to achieve what you are looking for.
Personally the tail on mine wags under heavy braking, but everything else is good for me, so i'm content with the tail wagging and using the back brake to dampen the speed that the spring can rebound if needs be.
Hope all of that makes sense, and good luck with getting it sorted :thumbup