How about renaming the dll's if they exist, install the new dll's, install your software and register a small app to silently kill the renamed dll's at next reboot (but the user does not have to know)

Good idea, but not an option. Doing that way would defeat the internal routines that InstallShield uses to check DLL versions and increase lock counts, which determine whether or not it overwrote the DLL and whether or not to erase or leave the DLL at de-install time. I would hate for someone's system to stop working when they deinstalled our product because it also deinstalled SHLWAPI.

I will also check that utility you linked, thanks.