I know of two ways to reduce rocker in a driftboat. One (the more complex method) is to dish out the chine edge of the side panels (so they are no longer a straight line when the side panel is lying flat on the shop floor). That method is what most of the following pages (links at screen lower-left) talk about.
The other way to reduce rocker--at least at the upstream, transom end--is to widen the transom. This is something you can experiment with in the beginning stages of construction. In other words, if you have a stock set of plans you are workign with, but you want your boat to have a bit less rocker at the upstream end, make the transom 3-6" wider. That will drop the transom down closer to the water. But beware. You do need an absolute minimum of 8" upstream rocker. Some people (Ray Heater, for instance) will tell you 10" is a minimum. The HD is about 12" the way it builds, so you can reduce it a tad if you want. Play with and measure it and proceed judiciously. The curved-chine method (the way Rogue River Boats are built) follows from here. If you want to reduce rocker at the downstream end (you can reduce that a lot more) you will have work with a dished-out chine.