I built a simple installer in Wix which will place a couple of data files in a specific folder in a preexisting product installation so that the user doesn\'t need to know anyth
There are two types of environment variables: user environment variables (set for each user) and system environment variables (set for everyone).
By default, a child process inherits the environment variables of its parent process. Programs started by the command processor inherit the command processor's environment variables.
https://msdn.microsoft.com/en-us/library/windows/desktop/ms682653(v=vs.85).aspx
Probably, you can check machine users and if product is installed for all users point to system environment variable in Local Machine.