There isn't a way to send symsched command line from the SEPM strictly as a command (or through using "Run command on group" in the Clients tab).
However, scheduling LiveUpdate and scheduling virus scans through policy in a managed environment writes exactly the same information that the symsched command does. See the screenshot for the result of what the Virus and Spyware and LiveUpdate policies write on the client side by default: every four hours for LiveUpdate; every week on Monday at 8pm for virus scan. These schedules are not visible in the SEP client side when clicking Open Symantec Scheduler, because it writes the schedule for all users in the root account.
In other words, it already does what you want it to do by default because it is a managed client. If you want to change the schedules, change the policies. There is really no reason to make things more complicated. 
I hope this helps.
sandra