So, if I understood everything right, the trick is to move nvidia.o from /lib/modules/my.old.kernel/kernel/drivers/video to /lib/modules/my.old.kernel/misc, because that directory is in modprobe's path, too, but it's not recognized by NVIDIA's "auto uninstaller"?
Then I just have to boot the new kernel, run the installer and I should find a new nvidia.o in /lib/modules/my.new.kernel/kernel/drivers/video
It doesn't seem difficult. It could even be generalized for a thire or fourth kernel by playing the same trick over again, am I right?
does the other trick (manual decompressing and make/make install) give exactly the same results? This seems even easier and generalizable for n kernels.