I’m imagining the cross section look something like a 9, where the top loop is where the pen goes and the bottom hook goes into the back page of the journal.
This is my solution at the moment. I’m using the “pen trick” for bullet journaling. I hate it. The tip of this pen(cil) is very sharp and I don’t want it to get damaged. It catches on just about everything. And it puts pressure on the elastic.
What I would like is something like this but with a tail so that it fits into the back page of my journal nicely. (this is more of a C shape, and I’m looking for a 9 shape). I’d also like to to be more tightly bound and only needs to hold one pencil like this (however, I believe this one is part of the cover. I imagine you’d need fairly thin leather to make it fit nicely into the back page of my journal and I don’t know if that’s going to be a challenge (thinness vs durability). It might need an extra layer of material around the tip to keep it from poking through.
I’m betting you’ll need to measure the pensil itself to make it fit snuggly. I’m not sure if the clip should go clip over the leather or have a U shaped cuttout for the clip to go. But I’m betting that depends on how snug the pencil fits.