do a search for cb400f race project and you'll get my project thread toward the top of your results... toward the end of the thread are many pictures of what i did to accomodate a passenger (like i'm ever going to have one!) and keep a racey look... compare my end product to a cbr600 f2 or f3 seat and you'll figure out my inspiration.
check my gallery link in my signature and you'll see a true cafe seat w/ hump on my 350f
... both seats were cut down from stock and reupholstered. use marine grade vinyl for lasting looks and weatherproof-ness... found quite economically at most fabric stores.
edit:
now that i'm not on my work computer... i'll just link to some pics for you...
73 350f cafe
73 350f fair'd cafe
75/77 400f race project (seat before)
race project (seat during)
race project (seat during)
race seat
race seat
race seat