I just installed a roller on my MH Tempest about a week ago. I think it turned out great!
I slapped my control panel on the scanner and then in photoshop placed the 2.5x2.5" (iirc) square with the top edge following the top edge of the hole left by the spinner. Printed it out and lined it up with the control panel art so I could perfectly transfer the pattern to the CPO, then drilled the corners and cut out the square with a saber/jig saw. After filing the edges of the square to make them a little more straight it looked pretty good! I only drilled two additional holes for the roller mounts -- I found that you can re-use the spinner holes and just use some large washers to pin down the top edges of the roller housing. It is extremely tight and solid now and I'm not left with two ugly bare holes where the spinner used to be.
It bothers me a little bit that the area under the spinner knob has a permanent circular wear pattern on it, but I don't think it can be avoided?
As for the crystal thing, I was worried about it as well but the roller seems to work great for me with no modifications. It's nice and responsive.
Anyway, here's a photo: