Thanks to all who responded to my post of 7/8/2012. Lots of ideas
I tried Sonny's thought on applying moisture and pressure to the
convex side of the panel. I scraped off the old glue, used the corner
of a card scraper to cut some shallow (~1/64) relief cuts along the
panel grain every inch or so. I used some short dowels in a hunk of
CDX to support the panel only (not the frame) at the corners of the
concave side, then put some folded wet cloths on the convex side. Some
scrap 1x3 was used as cauls across the grain at each end and in the
middle. I started with 10 pounds of weight on each caul, then after 2
days increased it to 25 pounds each, then 2 days later to 50 pounds at
the ends where the cupping was the worst. No heat was applied, just
left it in an 80 degree room.
After 6 days a lot of the cupping was gone. The panel wasn't "flat"
but the cupping has decreased greatly. I then let it dry, still with
the weights on it for 4 days.
I had to relieve the front edges that went into the frame dado just a
bit with a chisel to get the broken trim edge back in place. Glued
that back in place along with the split trim edge (not glued to the
panel!) and glued the back (writing surface) back on. All seems OK, no
movement of panel wood, so Monday it goes back on the desk.
Once again, thanks; even if there were those who found the original
thread anally retentive, it was helpful to me.
Pics on A.B.P.W if interested