Since inno v6, there's been a way to provide an optional, noninvasive way for users (if they want to) to install for the current user only. If you look in the release notes here for "Overridable Install Mode" they have a decent explanation.
https://jrsoftware.github.io/issrc/whatsnew.htm
Once it's set up with
PrivilegesRequiredOverridesAllowed=commandline
The user can set the /CURRENTUSER switch on the command line to install without elevated privileges.
There are path tokens that have to be checked, as they talk about in there, but it's a relatively painless process to create a setup that runs either the way it runs now, or with the override switch if someone asks for it.
I can understand completely why you wouldn't want to mess with an installer that works