I know I am reviving a dead thread, but google brought me here.
I was going to try and do a similar mod to my thumb trackman with a Redragon Mammoth for 16400 dpi. It seems like I keep the internals of the high dpi mouse and put them inside the trackman, then point the laser at the trackball, which should be painted, and then invert one of the axises.
Anyone have any tips?