ISTM there may be two ways to fix this problem; one was to change the
.exe header produced by bdist_wininst, but in retrospect, it can't fix
this because it's likely Windows' 64-to-32 bit conversion (Wow6432Node)
that's changing the registry path used, rather than anything that Python
or distutils is doing.

The other way, which has more probability of working, is for the 64-bit
Python installer to include an extra registry entry that would allow the
32 bit versions to find the 64-bit version.

(This might also require an install-time 64/32 compatibility check being
added to the .exe header for bdist_wininst to prevent installing
binary-incompatible extensions.)