if you want you can try my diverting software for emontx shield I could easily set it up for that that it turns on and off a relay for secondary devices as it has relay support built into it
I can easily adjust for that situation … but I update sometimes today as it currently has auto relay support on the third ssr I make that support 1,2 ,3 and 4th ssr depending on what amount of SSRs you choose to use