Finally got around to working on making a base for the straight key. I cut off a section of some 1x4 lumber, sanded it nice and smooth, beveled the edges and covered it with a few coats of clear gloss polyurethane.
A little bit of sanding after the polyurethane finished drying and on went the straight key.
For some grippiness so it doesn't slide around on the desk, I spray-glued a piece of some rubber shelf liner to the bottom.
It's not a heavy base, and I might decide to change it later on to something more interesting looking. For now, it looks reasonably decent and gives the key a slightly bigger footprint and elevates it a little bit for more comfortable use.