Wait for finishing a logout script before logging out / shuttingdown

Hi,

From win7pro I need to run a 3rd party file synch application
(mysynch.exe) from a vbs script invoked from a domain GPO's User Logoff
Script folder.

Is the user has selected Shut Down instead of Log Off, the script would
actually run when windows has started the process of shutting down.
Hence I wonder how to call mysynch.exe from my vbs script ensuring that
windows waits until this process has finished before continuing the
shutdown process (i.e. which parameters to set, and other possible
issues in this situation)

I crosspost to vista.general to have possible comments about other
techniques to safely run and wait for applications at logout / shutdown.
Thanks a bunch for help on this

regards

Tor