I've tried Tweak UI from Powertoys but it shows that I'm already using H:\ for Programs. I've done a quick hunt through the registry and see that I have about as many instances of G:\ as of H:\ - in other words it's all a bit of a muddle and I reckon Sephiroth's advice to live with it is probably the way to go.
As long as everything works - good. I personally install as little as possible on the ROOT drive - makes refomatting a little easier.