The first part of the install should be a .msi application object and .msi installations are automatically performed as the system user, except for "Current User" parts of the install. When a .msi application object installation runs, you will normally see at least 2 instances of msiexec.exe running in the task manager. One runs as system, the other runs as the user logged into the computer. If the .msi install itself is created properly, it should install as the system user and then register the printer components for the logged in user. Unfortunately, few .msi packages are created properly, which makes our job much more difficult.
For the second part of the install, if you run as unsecure system, won't the same problem exist as the original install, where the printer object will be installed for the system user rather than the logged on user?
Also, unless user interaction is required, IMO using unsecure system user is a bad idea, use secure system user instead.
Note: These are just observations, I have not tested this procedure myself.