I saw a rather interesting tool on eBay for disassembling Pelikans :
I cannot comment whether this is the appropriate tool to use compared with some of the knockout block assemblies that we've seen over the years, but I was fascinated with the video. It appears from the video that the barrel screws into the tool, so as to retain it when the piston assembly is being removed. Part of the tool appears to be wood, part steel. Pretty obviously, this is only valid for certain models of Pelikan (and is so noted within the ad, "Tool for disassembling Pelikan 120, 140, M400, M200"), but it did seem to be a solution that could allow for a modest amount of force instead of a solid whack to the piston assembly.
US$65 (including shipping) is a bit steep for me to entertain this just to play with it, not forgetting that I do not pretend to be a pen engineer/repairer ! Still...