I finally found a mirror to replace my folded passenger side mirror. It's a bike mirror, got it in a Decathlon sports store for 24PLN ($8/6€), and it is mounted on a ball joint:
I removed the part that goes into the handlebar and placed the mirror at the front of the window, but - oh no! - all I saw was my side mirror, even though it was folded!
What to do, what to do? Thankfully, the plastic that covers access to the mirror's wiring comes off quite easily.
So I drilled a 4mm hole in it for the screw, added a washer, put some scrap rubber underneath (plastic against plastic/metal doesn't have enough friction to hold everything upright), and
presto:
(Yeah, that washer will get painted black when it gets a little warmer.)
I've actually killed two birds with one stone (metaphorically speaking): not only did I increase safety while reducing drag, I also stopped the Wife's complaining about not seeing anything when she's a passenger. In fact, maybe she'll start to drive without unfolding the passenger mirror, reducing fuel consumption even more.
Of course, the OEM mirror won't be removed, since I still use it sometimes (eg when maneuvering in tight parking lots, or when hauling a trunk full of cargo/people), and law requires a second outside mirror when the central, internal mirror can't be used.
BTW: The cable in the last picture is my coolant heater's extension cord.