Radiolink RC4G/RC4GS/RC3S 3rd channel button presser

I was using the RC4G for drifting. But I found the trigger inconvenient for braking - too much travel, and impossible to find the exact position for the right amount of throttle afterwards. So, I decided to use the third channel for e-brake (or fourth as Radiolink calls it, since it names #3 for gyro sensitivity).
Programming it was very easy, and the button was correctly set up for use as an e-brake: only active while pressed (in other radios the button works as an on/off switch). The problem