Found the old style more comfortable so found a way to mount to a 2011.  First I unstapled the rear vinyl of the passenger seat, drilled a hole, fabbed an L shape bracket and bolted to seat under the vinyl.  Pic shows long bolt only because this is mockup, going to recover seat later.  Relocated rectifier to side of battery.  Drilled hole through front of fender to allow bolting of passenger seat front tab.  Used button-head bolt and nut for lowest clearance above tire.  Then put on spacing washers and tightened second nut over top of tab and first nut so wouldn't have to worry about bolt falling out every time I remove rear seat.  Sissybar is backrest work-in-progress.

bumping this thread because i was thinking of doing something similar.  except, since i never do 2 up riding (i can barely ride with just me on it sometimes lol)  was thinking of building some sort of a bracket or 'deck' to mount a storage trunk in the pillion area.

use it for storage....a backrest perhaps....and mount a 2nd brake light to it.  was wondering what i needed to do with the rectifier or if i could just build the rack over top of it.

Yeh, I never ride a passenger either.  Cut the passenger seat down and recovered it, then bolted on a base for the luggage bag.  It's a quick on/off with 4 hooks to unhook.  Sissy bar is still work in progress though I do have a padded backrest on it now.

The seat on the backhoe is toast, rusted, holes in the seat pans, fabric shot, seams ripping,, it about 25 years old, so, its fair,Anyway, Im repairing it.. Went to an upholstery shop & for $25.00, got enough heavy duty material to fix it all up. The guy said its what he uses to make toneau covers & it will handle being outside,, Enough to cover a bike seat? Cant cost much,..

Yea JoAnnes's is a craft chain of stores if there are any near you they have a nice selection of marine grade vinyl in different grades, patterns and quality.  I just got enough to redo a workout bench and two bike seats for about $12, it's nice and thick and would cover two S40 seats easily.  They also have different types of stuffing/padding if you want to experiment with different types for a more custom/comfortable seat.