Uninstalling correctly under Vista

I'm just getting started with NSIS, and have managed to get my installer to use MultiUser.nsh to allow proper installation as "just me" or "all users". It puts the application (and, I assume, the registry entries) in the proper place based on privilege and asks the "just me / all users" question if the user's running as admin.

However, I'm stuck on how to handle uninstallation if the user installs as admin but tries to uninstall as a regular user. Currently, the uninstaller just says "Complete" but nothing is deleted.

How can I check for and handle that situation - either by just giving a reasonable error message or by requesting some privilege elevation?

Thanks much in advance for any help!