The A1015's I've owned and used (last one purchased about ten years ago) actually have an RF activated switching circuit installed, but disabled because that's not allowed by Part 97 based on the amplifier's characteristics. It's lawful for an amateur to modify the amp to enable the RF COS (carrier operated switch), but they can't ship it that way.
You have to open up the amplifier and observe the PCB, and add a connection. I haven't done this in many years, but I think in my last A1015 I had to add a coupling capacitor installed in two "empty" component holes in the PCB to enable the COS operation.
However, if you call Mirage on the telephone and ask, the "routine" used to be they'd ask for a copy of your amateur radio license (which you can FAX to them, etc) and then they'd send you the exact instructions.
Otherwise, the "hard key" line as discussed above by Gary always works and can be found as an available "key line" connection from almost any kind of SSB 6m rig -- but most "FM only" rigs don't have anything like that.
What if soy milk is just regular milk introducing itself in Spanish?