Contact r550 and have him take pics of his seat for you.
A guy in Portland cut down and built up his stock 550 seat.
Not exactly in cafe style, but could easily have taken it further, to build the boat tail hump, and lower the seat more, if Ryan had wanted.
Cost him like 100 bucks, and still works like the stock seat, because, well, it pretty much is.
I also had a seat done by him for a bobber kz440, he does a really nice job. Maybe you can send it to him and have it done. Even with shipping, it'd be less than most other options.
Or maybe someone in your area can do it.