You need to create a virtual sink!
To quickly test it, run:
pactl load-module module-null-sink \
sink_name=audiorelay-fake-speakers \
sink_properties=device.description=Fake-Speakers
Then select Fake-Speakers as your default output device or as an output for a single application:
Don’t forget to select Monitor of Fake-Speakers in either AudioRelay or Volume control.
Keeping the fake device after a reboot
Add this line at the end of /etc/pulse/default.pa file:
pactl load-module module-null-sink sink_name=audiorelay-fake-speakers sink_properties=device.description=Fake-Speakers
Let me know if this works OK for you. 
(I’ll need to add these instructions here. )