I created a feature request topic here: http://forum.kodi.tv/showthread.php?tid=308802
Then I figured out how to make the change. I’ve never contributed here before, so I hope I’m doing things right.
In project/Win32BuildSetup/genNsisInstaller.nsi there are two lines that set SetShellVarContext to current, one for the installer and one for the uninstaller. Per NSIS documentation I changed those lines to set SetShellVarContext to all. This changes the installer context to all users, resulting in shortcuts and uninstall registry entries being created for all users. We require admin privileges for install anyway, so this makes sense. Most Windows apps use a rule like this: if admin privileges are used for install, the install is done for all users. If standard user privileges are used, the install is done in the current user’s context.
I created a windows-installer branch on my kwade00 github account, made the changes, and made a pull request against the main repository.