We wanted to use Update Manager right away when we upgraded from 3.0.x to 3.5.x to fix the tools versions until we realized you need the version of VMWare Tools that comes with 3.5 installed already to add the service so Update Manager could scan the VMs :smileysad:
We opted to use the VI Toolkit to script the install instead. If you don't have this installed in your environment already there is some upfront to get there but not much (.NET 2.0, Powershell, VI Toolkit install) but the options offer full automated management of almost anything VirtualCenter can see. As for your specfic request, the info you seek if you go this route would be here.
http://halr9000.com/article/642
-Mike