I don't have that controller so this may not be 100%. I believe you can set the limit on the controll to 110% for Ch3. and use the mixer to set the prefered switch to send 110% signal to CH 3. This way the switch fires the gun but pushing up and down on the stick wont as long as you have the trim zeroed which you would since you have servo for elevation. BTW you really need to have the centering spring kit so you dont fight to keep the gun from moving.