To clarify, you’re wanting to pull data from the selected option - and it is not the Value that is stored in the EpBinding or the Display Text?
Unless somebody is aware of a native way to do this, you might have to retrieve your third piece of data from the BAQ - calling it with a Where clause to specify which row you need.
Or you could execute your BAQ and store it in a data view, then have the combo refer to the view to populate its data… I’ve never used this method, but I see it in combos in the some of the base screens.