Thank you, thank you!
The basic idea came from Al / Tapla of "pine bark gritty mix" fame. He talked about wicks even though he thinks they usually just make up for the drawbacks of poor container mixes.
Since i used to ALWAYS overwater seedling trays, I knew that I needed something to pull excess water down and out of the tiny cells. My fi4st try was some synthetic "batting". The loft and fuzziness was good - it made good contact with soilless mix through small holes in the bottoms of inserts.
But batting was very bad in terms of getting dirty and falling apart into fragments in a few weeks or a month of use.
Cotton flannel turned out to work well. Amazingly, it even seems able to reach through thin "burned" slits in "1206" cheap 72-cell trays (twelve tear-able six-packs with skinny drainage slits).
At first I was only using it to cure overwatering: I would top-water to excess as usual, and water would then be pulled out into the mat. Mission accomplished.
I kept seeing ads for cap mats used to distribute water to all the pots on a bench. And I could see that the water from some over-watered cells was being distributed by the flannel to the under-watered cells.
Eventually that combination of simple things that I already knew penetrated into my brain and became an actual thought.
I realized that I was already bottom-watering the "dry" cells without carrying flimsy trays hither and yon, and without getting my bathtub drain clogged with perlite, grit, bark and peat..
So I cut one 72-cell out of one corner, and began bottom-watering instead of top-watering. That worked, too. And the soil surface stayed even drier than my coarse bark mix was already achieving.
I can't take any credit for smarts, here. It was more like discovering that a silly work-around for the bad habit of over-watering had a side benefit ... bottom-watering and water-sharing by default.
But I will definitely and proudly keep the acorns and thumbs!
P.S. I'm still looking for material for home-made capillary mats that never rots, lasts forever, has lots of loft and water-holding capacity, can be washed and is as cheap as possible. Maybe something with microfibers and other synthetic materials. I'll be testing some kinds of felt (when I get around to it, one of these years!) Any ideas would be very welcome, or sources of commercial cap mats that are cheap.
and fat wicks