Well... located an unopened package of "Loctite Plastics Bonding System" in the basement. A two-part, basically some sort of "activator" (in a felt-tip marker) and some variant of superglue.
I can't even tell if the activator still has anything in it (no damp mark running it across a finger nail) -- if I interpret the package warning, the activator is heptane.
Rubbed the activator across the two parts, waited the 60 seconds, then rubbed the superglue over the barrel end, pressed together, and held for 30 seconds (per instructions).
Then lightly (?) screwed the cap on while digging up my shopping list from the next room.
Came back and couldn't get the cap off -- apparently the 30 seconds wasn't the drying time, but just the set time, some of the glue that seeped along the edge bound to the cap. Took two-three minutes of hard twisting to get the cap loose. The glued crack held through all that torque.
However, I still intend to just make that a free-roaming desk pen, not a carry pen. Broad nib, so fits my idea of a "signature" pen, and I computer-print checks right next to the desk.