The priority queues also need a stretch of not super-curved space on the main queue line in order to attach. So if you're a fan of curvy queues make sure to leave it mostly straight (or at least a very shallow curve) wherever you want the priority line to enter and exit.
The priority entrance and exit have to be placed on the existing queue path and then you join them up with a path, so the priority pass holders get to jump some of the queue, if you take a look at the sort of ghost train ride on the 2nd pirate scenario in carreer mode there is already a priority queue setup, take a look thats how I sussed out how to do it.
The priority queues also need a stretch of not super-curved space on the main queue line in order to attach. So if you're a fan of curvy queues make sure to leave it mostly straight (or at least a very shallow curve) wherever you want the priority line to enter and exit.