Bring it out to a 2 pin header with ground and put a jumper on it for now to hold the regulator on. Remove jumper, connect logic output and you can then switch the power to the VFDs on demand. If you decide to put a pullup there to 27V like the datasheet shows, put it on a 3rd header pin! If you use a mechanical switch, you can connect it to both the pullup and ON/OFF, but it avoids the logic getting 27V stuffed up its chuff which it wont like much.