The simple version of the answer is that you can't, this applies to all brands of programmable rx not just weatronic. Any rx mixer is permanently on, because the only way you can send data to the rx is by using one of the control channels, so to send an on/off command to an rx mixer would use one of your channels. This leads to the cmplex answer which is that you can, by switching on and off at the tx a channel which sends an opposing travel signal to cancel out the one the rx is mixing. Therefore it is technically possible with simpler mixes, but is far more complex to do and consumes a precious channel so is somewhat pointless.

The english language manual is on the front page of the english version website, at the top left. It's not in the download section which is where you would expect it to be!

Harry