In talking with a couple of other RV owner/builders in the area, neither of them have any "quick" remediation for runaway trim servos. It's clear that it's standard practice to be able to quickly disconnect all autopilot servos, but not necessarily the trim servos. I understand that there's a flight test to control the plane with a stuck trim, it's not something that's easy, but it can be flown.
I have an Aerotronics panel that was ordered by the previous builder, and it does not include a trim servo master switch, and also has an EXP Bus that uses solid state current limiters, meaning no physical CB to pull, even it you did catch and realize that a trim servo was "running away".
Is it actually more common to wire the trim servos, without a master switch?