On the provider side there is a circuit connection already. Would it be possible that depots / liquid depots connected to the circuit network respect some external circuit signals? I am thinking about signals similar to "provide priority" and "provide threshold" from LTN. Heck, you could even re-use the same signals so people who have both mods installed to not clutter the virtual signal menu even further.
That way you do not need a GUI, and for guys who do not require this feature, nothing would change.