You can make something like kurplop's ErgoDock and then tent it any way you like it, you can even embed tripod mounts in the dock/tray.
A way less involved option is to simply cut, say, closed-cell foam wedges and lean the keyboard halves against them.
Another way to tent a keyboard that I've seen is Kinesis V3 lift kit for Kinesis Freestyle, modified with some extra grips for other keyboards.
edit: You can also build a support construction from something like lego bricks.