Well, there is always Waterfi:
http://waterfi.com/waterproof-kindle
They sell waterproof Kindle PW1s (as well as several other popular devices).
You can also mail them your device and have them waterproof it (works out to about the same price).
Alternatively, you could jump ship and get the Kobo H2O, but I hope you will understand my reluctance to advocate that in this forum.