You export the box as a separate IGS and create an Editor shape blueprint for it. These are objects only showing in World Editor. Then you make that a child object of the scenery object that is the bike or whatever.
Original information here.
I never tried that for the purpose of selecting scenery. But I can confirm that the visibility trick works, even if the editor-only object is child of something else. I used it as a placement guide for signals back in the day when they would not snap to align with the track.
I will need to experiment with this myself, it seems. My hopes that a collision box would help matters were not fulfilled.
I found though that you can select difficult object by dragging up a circle and after that, you can drag about the (new style) gizmo like you would drag the object. But you cannot select it by clicking on it, you need the circle.