Help Newbie: USRP Common Control or Backup Channel using Simulink??

Dear experts, I have tested the basic QPSK simulink model and perfect !!! I receive the Hello world msg in the command window.

I wonder if it is possible to create a backup channel for sending ACK/NACK or any other control information from Tx to Rx, something like a common control channel for feedback etc. If yes, may you please guide me with these steps.

would be thankful for your kind help.

Best Regards Usman Ali