I can't think of an easy way to use the Tamjets failsafe as you describe but you might be able to work around it.

Bear with me as I might be talking rubbish here but

The only way I can see that you could get the failsafe to operate 2 channels plugged into the Weatronic is if the output from the Tamjets failsafe is input to the receiver. The only 'input' that I am aware of, is through the gyro function. In this case the Tamjets failsafe would replace the gyro. I am not sure if you would be able to set up the sequencer function in the RX like this though.

I personally think that, if you want to use the failsafe, it would be much easier to use a separate sequencer.