I used little round blind spot mirrors that are mounted at an angle to the base. The angled part can be rotated to point the mirror in different directions, and this works ok. It seems like the convex mirrors aren't very sensitive to adjustment.
They're stuck to the upper window frame with a little L-shaped piece of aluminum and some 3M Automotive Badge and Emblem double-stick foam tape. The tape is good stuff, you can find it at automotive paint supply stores, and sometimes at a regular auto parts place.
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