I mounted a Spintrak at the top of the left bar of the large X. It's an OK spot, but not great. Can't rest your hand without pressing buttons. But you can rest your forearm below the buttons. And, I should have checked what was under that location before I drilled. The two front side buttons caused some interference so I had to add a small spacer under the flange of the Spintrak - lucky for me that worked.
I may look at moving it to one of the P1 or P2 button locations and move those buttons somewhere else.