I’m lazy too. The clamp on/strap on type pads are one more thing to remember to bring, one more thing to spend time bent over installing (or removing) each trip and one more thing to potentially misplace or lose along the way.
And I am phobic about anything permanently installed that protrudes above the top of the gunwales. I slide my canoes on and off the storage racks, and on/off the too-tall van roof racks. On the van, with four crossbars, any above-sheerline obstruction becomes even more maddening.
My KISS inclination would be to take a piece of minicel, not much thicker than the top of thwart to the top of gunwales, cut it sized to the thwart width and carve out a center notch to accommodates that knobby vertebrae. A 2 inch x 20 inch piece of minicel and little contact cement might make for a permanent and inexpensive solution. Round off the right angles on the top of the minicel pad to reduce the sheer forces when slipping into the yoke.
If you want more of a sculpted yoke shape maybe screw in a couple of U wood shoulder protrusions and cut some yoke shaped minicel to fit. But none of that is really the original piece.
Truth be told, and I know you want to save the original “yoke”, my first inclination would be to install a new wood contour yoke and have something permanent and
very comfortable.
I really like the contour yoke Esquif used; broad and deep that sculpted piece fit my shoulders perfectly, including the vertebrae notch. Those Esquif yokes were also eye candy curvatious art.
Ed’s Canoe makes something similar, if not as elegantly sculpted.
http://www.edscanoe.com/copoyo.html