Just deleting vcbnames file from "C:\Program Files\VERITAS\NetBackup\online_util\fi_cntl" directory, allows netbackup to re create the vcbname file with updated informations.
So just schedule a Job in your server that will delete the files under that directory whenever no backup is active.( This file is accessed by Veritas when backup is active)
I just checked it my NetBackup Test Environment. It works good. Here the logs i got from C:\Program Files\VERITAS\NetBackup\logs\bpVMutil.
<2> get_VM_names: get_id_lock returned 0
11:57:59.509 [1868.3344] read cache file = C:\Program Files\Veritas\NetBackup\online_util\fi_cntl\vcbnames_**.***.***.***_Any
11:57:59.525 [1868.3344] cache file C:\Program Files\Veritas\NetBackup\online_util\fi_cntl\vcbnames_**.***.***.***_Any does not exist
11:57:59.525 [1868.3344] getHostView: Getting VM's for 10.237.204.134
Try it and let us know !