Hi Sergei,
you sure can use the I/O switching, just put a timer at the remote end that switches off after 50mS
when you dont use the build in keyer its easy setup.
When you need the keyer then there are everytime a few things you have to do
disable keyer at control end,
put OUT0 mode at RADIO end to I/O and close input 0 (control side) to gnd when you need to start K3
afterwards you enabl keyer again
Guy ON4AOI