I wouldn't recommend it, but you could conceivably install one for the system and one for the individual users. You can try it with the following commands.
System install:
msiexec /i Proximity.msi /qb! DISABLEAUTOUPGRADE=1 LAUNCHPROXIMITY=0 ALLUSERS=1
User install:
msiexec /i Proximity.msi /qb! DISABLEAUTOUPGRADE=1 ALLUSERS=2 MSIINSTALLPERUSER=1 LAUNCHPROXIMITY=0