As an FYI to others out there, we ended up using the recommended Group Policy login script from MS and modifying it to run the three installers in one script. Not exactly what I wanted, but it works. An additional consideration is that we had set our max logon script time to be 10 minutes in GP, so if it was trying to remove an old version of Office or it was a slow computer, sometimes it would not finish and I'd have to do a manual install anyway. 95% success rate is good enough for me though :-)