Wow, to me that's pretty ingenious and nifty "tweak".
Haven't done a lot of skin editting, but I just paste the above to the ExecTBL.ini file (like you said), and then on whatever skin page I want I add a button called FLIPFLOP, that about right? In the actual .skin file you only have the button defined and the labels, right?
Labels on and off
L,882,96,100,20,72,72,0,14,"Arial","BYVAR;FLIPFLOP SET;=Flip - Flop<<","LEFT"
L,882,96,100,20,255,255,0,14,"Arial","BYVAR;FLIPFL OPSET;<<=Flip - Flop","LEFT"