Ubuntu Studio Controls: How to add and map surround audio channels to a pulse output bridge?

I am using Ubuntu Studio 20.04 with JACK through ubuntustudio-controls. I have a surround speaker system and must change the default pulse_out bridge sink from 2-channel stereo to 4-channel. The four channels must be mapped to front-left front-right rear-left rear-right. This does not seem to be an option through the GUI.

Alternatively, I can add an additional 2-channel Output bridge, but the channels would still need to be mapped to the rear speakers. There doesn't seem to be any way of doing that either.

Making a single 4-channel output bridge would be preferable.

This could normally be manually configured through pacmd load-module module-jack-sink sink_name=Surround client_name=Surround channels=4 connect=no but Ubuntu Studio Controls wipes out any manual changes once "Start or Restart Jack" is clicked. If no solution is available, it seems avoiding Ubuntu Studio Controls would be the only option. Sadface.

I can imagine this would be an important feature since many professional musicians, studio engineers and audiophiles have 5.1 and 7.1 surround speaker systems, but the wiki page has no information on the subject.

How can I configure the number of channels in an Output Bridge through Ubuntu Studio Controls?