Attaching the flue

[This lass builds UK]

Hi all, I've bought a 500mm pipe for the flue. I think I was going to try and attach it between the exterior arch and interior arch at the front of the oven. I haven't actually got to this stage but foreplanning first. Do I need some sort of base plate under my arch to attach the flue to? Will the pipe stay if I mortared it in and use some support until the mortar dries?
If base plate, do I screw it into the arch bricks? Many thanks all