Add the ability to turn the Master Valve On Selectively, based on which Valve is On. So, if I want the Master Valve On for Valves 2, 3, and 8, but Off for all of the other valves, I can do so. I am hoping that a software upgrade is possible in your Revision 3 controller.
You could control the master valve programmatically, with a script that turns it on or off at specified times, or with a relay that enables the master valve when specific zones are running.
To control the Master Valve I used a couple of these relays so that the master valve only goes on for four of the valves
Electronics-Salon 1PCS Dual SPST-NO 10Amp Power Relay Module, AC/DC 24V Control Voltage. https://www.amazon.com/dp/B01B60RZPA/ref=cm_sw_r_cp_api_i_CxpoDbRJ5XDXY