RE: SD-10G stick switches
The short version is that it's not possible for the reason you described. That said, there are some solutions. Ideally we have 4 snap conditions right/left positive, right/left negative. There are really several limits on the SD10 for this situation (two of which I'm hoping will be addressed in some future software upgrade). The first is that the stick switches are not bi-directional, meaning that you can't assign it to turn on at 80% deflection EITHER left or right, up or down. Regardless, I've found a "workable" solution that you might try.
It still requires one traditional "switch". I set my stick switch to turn on my Snap conditions when my aileron stick passes 85% (my personal preference for when to do it) AND when the other switch (choose a switch you find easiest to flip) is on. What this does is allows me to flip the standard switch anytime prior to the snapping maneuver, and then when it 's time to snap, going to full aileron puts me in snap rates which for me changes the throws on all my control surfaces.
In flying the F-11 sequence, this allowed me to enter the Snap/reverse 4/8pt roll with my switch on, but flying normal rates. Perform the snap which would increase the rates when I went to the corners, and then still have low rates for the 4/8pt roll (assuming I didn't use full Aileron) and then turn the switch off later.
Hope that helps...