Hello,
It is possible to kick off a manual backup of a client listed in a policy on the master using the Windows Admin Console. To do this you would right click the policy and select manual backup. This isn't, however, what most would consider a "user" based backup. Most of the time when referring to a "user" based backup, the job is initiated from the client itself.
If you are logged onto the client, you can open up the Backup, Archive, Restore GUI and run a user based backup. The client would need to be configured in a policy with a user based backup schedule defined.
As for automation, the command %installdir%\NetBackup\Bin\bpbackup.exe can be used to kick off user initiated backups from the command line. For more information, please see the command usage guide located inside the "Veritas NetBackup (tm) 6.5 Commands for Windows" page 42.
http://seer.entsupport.symantec.com/docs/290235.htm
Thanks,
Kris