I bought a really cool "Boat tail" single seat for my RK that works it's way back to the screw and covers most of the fender but still is definitely a single seat.
It also works great with a sissy bar bag (sitting where the passenger usually does) when I go on a trip with just "The boys"...........mine is a Corbin you might want to look at them on their website
I got a black leather 'fender bib' from Mustang. It extends from under the solo seat, to just past that single rear fender screw hole, and has a hole in it for you to put a screw in. I just got one of those knurled seat screws that can be hand-tightened, and it looks just fine that way. I got the chrome screw, but you could get a black one and it would be even more inconspicuous.
I got a harley branded rear fender plug. Priced high for what it is but is black and does not pop out.
Blends in good. $10.00 for a small plastic plug did seam a little ridiculous though.