http://japan.webike.net/products/20409041.html

Kawa W800/650 Short Seat

A short seat if you need to be two on it, and not the complete family with childs, etc...
These two shorts are for sale.
They plug and un-plug exactly like the stock seat, nothing to add, change, or fix.
Unlike many (if not all...) W accessory seat,
you dont need to remove the metal hook parts from your stock seat,

making it almost unsoldable.
Now you can sell your old stock seat and have thiss money back.
Make your calculus and guess where is the bargain.