Armin, it’s not hard to do, it just takes a bit of practise [If an old dog like me can do it, so can you!]. Try it at home with your rig in practise mode. The 3.5mm to 2.5mm jack cable between the paddles and KX2 rig is 1m long [1.5m would allow even more freedom in operating positions].
My steel plate is 14cm x 6cm [7cm would have been better]. You don’t need to put a lot of pressure on the plate with the middle, ring and little fingers because a) the bottom of the plate is somewhat constrained by the bottom of the pocket, and b) [of course] you are paddling very gently with your index finger and thumb.
Obviously I can’t show it inside the pocket. The side pockets of my North Face jacket aren’t deep to get the wrist-end of my hand completely inside the pocket whilst keying but the keying fingers are snug and warm.
73 Andy