Thought I'd offer up my version of a solo seat. I'll blame Brun for the inspiration to build mine, although I still think his looks better. I'm generally pleased with the look but not quite 100%.. It took a couple tries with changing foam shaping and height to get to this point. I built the steel pan that is located by a thin notched "tongue" to a stud about 1" tall installed into an existing hole at the back of the frame's backbone tube. It also is held into position with a pin into a existing hole (that yet need a grommet for better fit) on the right side, and it latches into the stock seat latch on the left side. Padding and re-padding was done by a upholster friend who then eventually sewed up the cover. I'll get to work now on a small diameter tubing or solid rod luggage rack to extend over the rear fender.
Here 'tis. Cardboard backdrop was used to hide top secret things going on in my personal "skunk works". Ok, actually it's hiding the clutter on the other side of the bike.