Time to officially throw in the towel on this idea. My first incarnation held a slight bend, but not enough of a contour to match the rear frame loop:
So using the "get a bigger hammer" theory, I used a bucket of boiling water and soaked it for a longer period of time. This degraded the wood so that it began to delaminate, not a huge deal because the center layer is still thick enough, but it deteriorated as well and cracked a bit. I thought that switching grains may help, but that didn't work either.
Not to be outdone, I tried the skateboard laminate epoxy method with two layers of wood, but it did not provide enough of a curve for my purposes either.
So, saving an hour trip to the metal supply place turned into many hours of labor and several "mulligans" to no avail. Should have used steel in the first place!
I suppose I could slide the slightly curved laminated piece forward a bit and make it work, but I kinda like the idea of having the rear of the seat cushion kick up a bit, not just the rear frame loop.
Going to think on it a bit...