The feed and point knock out the front in the traditional way. I made a cradle for the section out of Fimo, with a very broad front end on it so it could snug into a really big hole on the knock-out block without any danger of contact between pen parts and block. I also put a hose-clamp around the cradle to keep it from being split by the wedge shape of the section.
Soak long, and even more than usual it's a case of many many tiny taps with the mallet on the drift rather than one hefty smash. I think it took me a week to get it to start moving, and a couple of hours to get it loose once it had.
Funnily enough, stuffing things back in wasn't as much of a struggle. I suspect this is because with the section out of the cradle, there's no inward pressure being generated.
I'll try to remember to take a picture of the thing; I realize the description is not entirely adequate.