I've hooked up the Dropsafe system with A2 controller and have outputs from D2/3 (ch 11 and 12 on TX) as safety and activation channels (RC1/2 on Dropsafe board) rather than running another receiver/transmitter.  Everything works as advertised and tested ok.  I'm not using Lightbridge and have Futaba 14SG linked to A2.  However, this setup lacks the protection that running a separate receiver with backup battery provides in the event of the loss of main power supply whether bad battery or connection.   Not likely but a contingency that needs to be addressed for commercial work.  
Plan A:  Is it possible to supply back up power to A2 controller via battery hooked up to the SB/X2 port without destroying the controller? It would be great if could hook up the Dropsafe back up battery into the A2 X2 port for backfeed on loss of power to X1 port from PMU/main batteries.
Plan B: If I use SBUS receiver and hook up to A2 via SBUS connection and set receiver mode to output ch 9 and up from receiver ports 1 and up, can Dropsafe's backup battery be hooked up to one of the receiver ports without backfeeding to A2 X2 port through the SBUS cable from the receiver?  I could then hook up Dropsafe RC1/2 ports to ch11/12 outputs on the SBUS receiver  Put another way, would SBUS receiver act as protection from back up battery backfeed into the A2 controller?

I really don't want to run two transmitters as its just me or dual battery supplies to A2 with diodes.

Any other ideas?

I've hooked up the Dropsafe system with A2 controller and have outputs from D2/3 (ch 11 and 12 on TX) as safety and activation channels (RC1/2 on Dropsafe board) rather than running another receiver/transmitter.  Everything works as advertised and tested ok.  I'm not using Lightbridge and have Futaba 14SG linked to A2.  However, this setup lacks the protection that running a separate receiver with backup battery provides in the event of the loss of main power supply whether bad battery or connection.   Not likely but a contingency that needs to be addressed for commercial work.  
Plan A:  Is it possible to supply back up power to A2 controller via battery hooked up to the SB/X2 port without destroying the controller? It would be great if could hook up the Dropsafe back up battery into the A2 X2 port for backfeed on loss of power to X1 port from PMU/main batteries.
Plan B: If I use SBUS receiver and hook up to A2 via SBUS connection and set receiver mode to output ch 9 and up from receiver ports 1 and up, can Dropsafe's backup battery be hooked up to one of the receiver ports without backfeeding to A2 X2 port through the SBUS cable from the receiver?  I could then hook up Dropsafe RC1/2 ports to ch11/12 outputs on the SBUS receiver  Put another way, would SBUS receiver act as protection from back up battery backfeed into the A2 controller?

I really don't want to run two transmitters as its just me or dual battery supplies to A2 with diodes.

Any other ideas?