Thanks, all. Scott from Loki recommended using a propane torch to heat it to launch temperature, then use the bulkhead to knock it out. I don't have a torch, so I have asked Scott if heating it in the oven wouldn't do the same thing. Waiting to hear back. May end up buying a torch ($18 at Home Depot vs. $45 for new casing).
This was the only time in my HPR career that I made these two mistakes at the same time: forgot to grease the liner, and didn't eject the liner while it was still warm from the launch.
I will let you know how it goes.
Oh, BTW, I don't think freezing would help because the liner is really heat-fused to the metal. Like glued.