Well, yeah, it'd not just be tying them to a stick. But they show that the people in that 'verse understand the concept of a shaped-charge (that, or an undirected packet of black powder is enough to do the job), so they should be able to work out how to make them. Seems pretty simple, just use a narrower cone of whatever it is around the head of a wood or bamboo staff, run the detonation cord back along the length of the staff (maybe have a couple eyehole screw-in bits to hold it?)
Of course judging by how things go it's apparently just as effective to behead the zombies as it is to destroy the heart. Why not shoot for the head (not really much different from trying to land a shot on the heart and hope it penetrates). If that's just a disabling wound, it still stops them from biting anyone or sensing anything so you can clean up later either by shooting the hearts until a shot penetrates or (again) using those primitive shaped charges.
Fair point on the rig he used... but they have man-portable steam engines, apparently, since that's what they use to power the guns. Why not run a band up from those to a neck brace and tightening band attached to the same (don't want to just have a band pulling the neck down, that's a good way to break the spine I'd think) so that if you get bit you or someone else can (say) flip a safety cover off of the triggering lever and use the backpack steam generator to power it?
Like, shit, kid was able to rig up that device and crude cartridges with scraps in his spare time. They apparently have the technical know-how to keep giant trains running with few/no problems, build use & maintain fucking steam-powered gas rifles, lay railroad tracks good enough that they don't need dedicated repair vehicles all over the place to keep them clear and usable despite everywhere being uninhabited save by murderous strong-fast-zombies and the tracks having heavy wear from the fortress-trains, build giant fucking steampunk fortresses in twenty years with what was apparently a pre-industrial tech base, &c...
I'm willing to buy the premise, but it'd be nice if they applied that generosity to more than the backstory of the setting.