you can program the m11 to have full steering when you hit the button. It wont be momentary but it will be a on or off thing. you set a c-mix so you will clone th steering servo to be like another servo.

c-mix 1
master=st1 slave=st
L=max offset=0
R=max c-mix=inh

set the c-mix 1 to what ever switch you like but it you will have to click it to turn it on or off.