Help me stop Yaw output unless throttle is up

Hey guy's, I posted in this section cause I need help with my config, tho it does work pretty well. Feel free to download and use it as-is (or mod to suit)

I set this up for the DSMX RX in my multiwii tricopters (I have 3 now) and on the 3D printed one's it's not an issue cause they have nice little legs keeping the small 6" props up high enough it's not an issue but on my big scratch built PVC tri it's so low to the ground the 11" prop on the tail will hit the ground if yaw is applied while it's sitting there. What I'd like to do it make it so the devo only transmits yaw data when throttle is applied but I'm not sure how to accomplish this... It wont take off till it's got about 25-30% throttle so I'm thinking for safety it could be setup to not apply any rudder till throttle is over 10-15%. Hope one of you fellas can help me, even if you dont want to do it I could work with an example I'm sure. I've just never seen a file with that behavior. Note I write all my files as text, not in the mixer, so if there's a really simple way to do this in the mixer I haven't seen it, if that's the case feel free to tell me to shut up and go look.

I've attached my .ini, thanks for any assistance!

Note 2 yes I did consider making it on a switch, but as you'll notice I'm using all 4 switches already and I thought this way would be more intuitive.
Switches are:
L_2-way = RUD D/R
L_3-way = SAFE/ARM/Buzz
R_3-way = Flight mode
R_2-way = AIL & ELE D/R


edit:checked the file and noticed (I pulled it from my HD, not my devo directly, its a slightly older backup) that it's still set to DSM2, I am using DSMX now so if you download it just take note. Everything else is the same (I switched RX's but nothing else)

Thanks PB, I appreciate it!

Unfortunately I was an idiot when I was thinking about this and it didnt occur to me the stick commands wouldnt work any more. Look's like I'm either using a switch or building some feet (the feet really wouldnt be practical).

How can I use a trim button to act as a switch to disable yaw? having it not work till a set %, while I still like the idea literally makes stick commands not register, I arm with a switch but I use stick commands for stepping threw telemetry screens on the OLED and also for calibrating the gyro's and for configuration.