It is possible from Powershell Jobs, except those 300 machines need to have PS Remoting enabled with force enabled and appropriate permission to take session, take a look at this.

http://social.msdn.microsoft.com/Forums/sqlserver/en-US/83190b71-a348-4a0c-85a0-a36ecf7db4a5/installing-sql-service-pack-by-powershell

Regards,