I've tried bottle cap WTCs before, if that's what you meant. To solve the problem mentionned you simply have to build an electronic component tray extending from the inside of the cap. That way, when you screw on the cap, the tray holding the electronics(wires, motor shafts) get screwed into the WTC tube instead. The only disadvantage with this system is that you cannot extend wires or linkages from the bottom of the tube (i.e: the other side of the WTC).