Yeah an adjustable height switch in the back would work too. It' all depends on how temporary or permanent you wish to make this mod. I'm just going by what I'd do, and I would drill a hole in the back of the sled and adjust the switch so that once I started to pull on the Empeg it would open the circuit and shut off the amp(s).

Just a thought does anyone know if you short to ground just the lead going to the remote turn on of the amp if it will shut them down faster or maybe instantly (or maybe kill the amp). So you'd have a switch that disconnects the Empeg from the amp then connects that lead to ground leaving the lead coming out of the Empeg just hanging so to speak.