The are two possible ways to do this:
1) Configure the sma service to run in safer mode. This can be done for the spooler service, so may also be possible for other services too.
2) If VBS can be executed when running in safe mode, you could use a method to run a standalone inventory package that contains the custom inventory vbs, utilisjg the following article in order to gather the relevant information: http://support.microsoft.com/kb/837643