It would be really nice if there was a hotkey that allowed you to toggle subtractive bsp visibility in order to make it easy to select them in the view port. The subtractive bsp would get a special rendering treatment so that they could be easily differentiated from the additive bsps. Maybe they would only render the wireframe, but that wireframe could be selected.
Hi Richard,
I have entered the following feature request on your behalf UE-36725. Let me know if you need any additional support or information regarding this issue.
Steve H.