The Gig Script can see/respond to midi messages at the system level (prior to being used by widgets) so may be an option for you.
You need to set up an alias for your controller in Rig Manager to be able to use the Gig Script in this way.
Here’s an example using a gig script with the control change callback. Note the use of Rig Manager alias and the ‘Inject’ functions that change/pass through the midi messages that continue downstream to the rest of GP.