That lathe has a hydraulic chuck on it. So long as you have the head of the bolt against the backstop it will clamp around the head of the 12-pt. just fine.
The backstop is bolted into the chuck, threaded rod with two jam nuts and just adjust it out to get it in an area you like.
Sometimes I use the EDM and cut a shape into a collet to hold an odd shaped part, or make a collet out of aluminum to hold something.
The possibilities are only limited by ones imagination.
Tom