I too was disappointed that there is no flip/flop pin on the SL40.
I dedicated a switch on my Infinity grip for this as the SL60 (comm/gps) that was in my previous plane had it, and the SL30 has it that is going in the other RV8 that I'm building. When I called Garmin AT about it , they said there was not enough room on the connector(15 pin) in back and that the SL30/SL60 get that pin from the Nav connector (37 pin).
Not quite worth $2K+ for the flip flop capability. I'll use the switch for AP disconnect now.
I made Scott disconnect the stick flip-flop for the 430W at our last annual. We had a few instances where the passenger hit the flip-flop switch accidentally, and some were by pilot passengers so it wasn't always a situation of "they didn't know better". Since we fly from both the right and left seats, our passengers can be on either side. Fortunately, this never happened in busy airspace or on an IFR flight, but it could. The risk far outweighed the convenience for us.