Summary

Here's a quick 8mm keyboard riser for Contour Rollermouse Red. It is designed to slide into the built-in slot. I use a thin rubber non-slip pad on the bottom and top of the riser to keep everything from sliding around.
I use it in conjunction with risers for the rear (https://www.thingiverse.com/thing:1562782) to elevate my keyboard about 10mm.
This object was made in Tinkercad. Edit it online https://www.tinkercad.com/things/h9bV06yHqpP