Stern Seat Cushion / Backrest for Old Town HW 16'

Anyone know of a good seat cushion/backrest that will fit the narrow stern seat of my 16' HW model Old Town?
I bought a couple GCI "Sitbacker" seats, and they should work great for the bow seat, or on my plastic OT, but the stern seat on my HW is so far back that the gunwales are not wide enough (12") there for the cushion's 16" frame to sit down on my seats.
I haven't found anything online, so unless someone knows of something, I'll end up just using a plain cushion on that seat, and not have any back rest, unfortunately..

 

I sometimes make fore & aft seat backrests for my restorations depending on how the mood strikes me. I've gone through several designs, again, depending on my mood. You should be able to see how they are made from the pics. They consist of the backrest itself and two L-shaped wooden brackets that are screwed into the bottom of the seat. The backrest is attached to the rear facing part of each bracket via 1/4-20 hanger bolt & wingnut. The short side of this bracket is angled away from vertical so that the backrest is at a comfortable position. To remove them you just need to unscrew the wing nuts. One of the keys is to not have the backrest rise too tall as you don't want your arm to hit it when paddling.

 

Those look very nice!