What about some velcro? At RadioShack they have this velcro that I cam't remeber the name of that uses plastic rods with little plastic nubs on the end on both pieces of velcro instead of the "fuzzy side" and a "hook side". It holds really well and doesn't ever wear out like standard velcro where the fuzzy side gets less grippy over time. You could strap a stick of this plastic velcro to the bottom of the solid block at the top of the keyboard, if the adhesive didn't stick you could dremel off a couple rows of the little rods so that you could run a zip tie long ways across this top block.
It would be more then enough to keep the keyboard in place and you could put the little strips in different places, like the passenger dash, the center console, or wherever the keyboard finds use.