I found one this morning at the salvage yard. 1989 Volvo 240. I paid $10 for it!
It was a bugger to get off though. The owner and I worked on it a while. He decided to cut the seat since they were in really bad shape anyway. Once we got past the fabric and foam of the seat we could see that the headrest was snapped into a little mount that held it in place. It was mostly plastic so with a little pocket knife wittling, prybar leverage, and me pulling on the headrest it popped free.
This particular model has 2 tubes coming off the bottom about 4 inches long. So I'll have to find some way to extend this, AND mount it to the bike.
I think if you get it in place at the right angle it'll be very comfortable. The problem of it is, if you ever need to get to the battery or anythign this has to come off. Hyper looks like he may have several things to undo before he can take his seat off. I guess those factory buil backrests also have to unbolted anyway if you want to get under the seat.
This is definately a project that will take some time, and inginuity. May just be less frustrating to buy a factory rest outright but I am a cheapo, and my wife is even worse. So I have to at least try it. Maybe I can get it to work, withough being tacky looking.
I am open to any ideas to help get this guy mounted.