[Therion] How can I suppress white space around centerline stubs ?

Hello, For Fuchslabyrinth cave, we're using mainly morphed bitmaps. With the standard thconfig settings, centerlines carry a "white channel" along with them, blanking out any bitmap content near the centerline (see attached image). Is there a way to a) define the centerline so that the white space around it is not generated ? b) define centerline so that it is always drawn (e.g. not only the stubs) ? c) define centerline so that it is never drawn (regardless of "point station" definitions) ? Regards, Michael