Adding any User objects to the Master DB is a very BAD idea. There are many ways you could achieve the backups -

1. Schedule the Backups using SQL Jobs.

2. If your version does not support it, you can create a .sql script file for backup and execute it using sqlcmd from the command prompt.

3. You can even schedule a batch file in your OS which intern would be calling the SQLCMD command.

4. Use SMO as I have already suggested.

Hope, this helps!