I see bikes parked all the time with black trash bags over the seat but that's tacky. I know Corbin makes custom covers for their seats (or used to), can you check with the seat maker if they have something that looks nice? Other than some WD40 on the mechanism for rust, I'm at a loss. Maybe someone else has dealt with that opening.
I have a cover for my YoungGuns saddle, but never use it. I should since the ass indention holds water on the leather. I've been getting by with keeping a towel in the saddle bags to wipe off the seat before I leave. Not a good idea, but I'm lazy. lol