Hi Phil,
This doesn't address your question of a peep sight, but I have a process for shooting any non-telescopic sights that works for me.
Basically it involves cheap "reading glasses" from WalMart or similar.
This works for eyes that are aging and make reading things close up harder.
My reading eyesight went downhill around 40, and it really made me panic over shooting handguns and rifles with open sights. The sights got fuzzy, and I could no longer clearly see them well enough to shoot.
I tried a pair of reading glasses, and that was the key. I have a BAG of reading glasses in my range bag now, of all different strengths, and pull them out and try them until one allows me to see the front sight clearly. The target is a bit fuzzy, but then, all shooting manuals say it should be. I use the strength that just gets the sight in focus, but no more.
Works for me. If you want the ultimate, figure out the right strength and have it built into a set of bifocals. Of course that is expensive if your eyes keep changing.
WalMart reading glasses are cheap. Just measure how far away the sight is on a certain firearm, and then use a stick or ruler at the store to gauge clarity at that distance. Those reading glasses are cheap, so it is easy to afford several pairs of differing strength. I paint a different colored stripe on each to keep track of which is which.
Hope this helps someone. Best wishes, Marc