After trying a bunch of changes in device type handlers, struggling with GE add-on switch functionality, etc. I finally just wrote a piston that treats a group of dimmers as one entity. These lights will always be set the same, but ANY of the lights in the set can be used as the ‘master.’. There’s a timeout of 15 seconds so inadvertent bumps to an adjacent switch don’t cause issues… that can be pared down or eliminated easily if you prefer.
Hope someone finds this useful. I’d rather be able to do this through Groups in the device type handler as they are instantaneous, but this patches the hole for now.