The only mix your thumbs can't do is the elevator up full spoiler and elevator down full flaps or the reverse of these. I used to try to mix for KE with my Flip and could really only get it right for one air speed and rudder input. More or less rudder or speed and the mix was wrong anyway. I toyed with clipping my tips but my shaking hand dropped the Xacto knife. I removed these KE mixes and started flying the corrections. It took a couple of tanks to get used to it but I don't use them at all any more. I also removed all of my exponential and found everything much easier. Your brain nor thumbs work exponentially so the radio Expo just confused the correction issue for me. It takes a few tanks to retrain your center stick bleed but it is worth it. Just make sure you use a low rate for landing at first with expo if you need it. Save the mixes for the Elevator to Flap mixes that you can't do with your thumbs.

Theres my 2 cents.