Actually, I am also a bit neurotic with my Volvo, who isn’t? ;-)
I replaced the ashtray bulb with the backseat seatbelt reminder bulb, as it only comes on for a couple of seconds when the key is turned on. They were a direct swap, with no soldering or tampering required. This bulb not only lights the rear ashtray, but also the center console’s compartment! In my case, it stays ON as long as your headlights are on, so it creates a somewhat eerie glow to the backseat passengers at night. Once you remove the back ashtray panel, you could also adjust (if needed) your parking brake. It is a plastic nut that you turn by hand; never seen a car with such an easy and fast way to adjust the ebrake. If you can find the missing bulb, however, please let us know where!

Regards,
JGCBAIZ