I am in contact with Carenado, about this. I think we are out of luck. I am thinking that the custom panel is just a modification of the model ie, the cover for the default 296 gps. I am waiting to see what Carenado has to say. I can't find a custom panel cfg file. So that is why I'm thinking it is just a modification of the model file.
So I think we are stuck with the 2d pop-ups for the use of other radios in the Commander 114.