You reminded me. There was lanyard between the seat drougue gun and the back of the canopy. It was designed, L believe, to stop the gun firing unless the canopy had been jettisoned. It was in addition to the seat pins.
PN - To the best of my knowledge there was no 'restrictor' on the Vulcan ejection system, (though it is now 50 years since I worked on a Vulcan and am open to be corrected), the only such device I remember was on the Lightning where there was a scissor like mechanism that prevented the primary firing unit from operating unless the canopy had jettisoned and a lanyard snatched away the scissor device allowing the main gun to operate. In any event, such a device would not have been attached to the drogue gun which under the normal sequence of events did not function until the seat had already fired and started to travel upwards along the guide rail.