From what you just described, it sounds like you just need a chunk of wire to run from the frame of the touchscreen (maybe epoxy it on there?) to the frame of the GLCD...and that's it. If there is an issue with EMI, then that direct connection would effectively drain the field away, for lack of a better phrase...
Is the bezel of the touchscreen or the GLCD painted? Maybe that's why it isn't getting a good ground?