SVXs in Europe have a switch to raise or lower the antenna. It too goes in front of the shift lever, in place of the shift lock button / access cover, and only works when the ignition is on.
Picture, courtesy of svxistentialist (click for larger version):
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[ADDED: Another picture is
here]
The blanks next to the fog light and rear defroster switches can be made functional simply by trimming off some plastic from the button caps. They have longer legs that prevent them from being depressed, but the modules underneath already have the electrical switches. [ADDED: They don't have the electrical contacts. See discussion below]
I've always wanted to rig one up for my garage door opener transmitter. Using a "real" button cap would be better (the "squirter" cap would be a good candidate), because then it would already have something that would light up from a dash illumination backlight bulb. With a spare fog or defroster cap, you would also have the lower window that could be used for a second light connected to the GDO's "transmitting" LED.