Yep - Both buttons should work.
I figured it out earlier today. Threw a xor function on the buttons, then toggled the result.
Note that "piston" comes out of my postgui file.
Code:
net pistonbutton <= hm2_7i76e.0.7i76.0.0.input-27
net piston => xor2.1.in0
net pistonbutton => xor2.1.in1
net pistonresult <= xor2.1.out
net pistonresult => toggle.0.in
net pistonout toggle.0.out => hm2_7i76e.0.7i76.0.0.output-04
