While this is not related to CHDK (could be though) I remember when a year ago I read about a really creative underwater housing. The DIY involved two condoms (yep, you read it right), one over another, stretched over the camera and sealed with a bead of silicone. It was an A70 or A60 I think.
The DIY-er claimed the military uses the same method for waterproofing certain objects. I was interested in trying out the hack but since I dismantled my A70 the S2IS probably won't fit inside an XXL-sized thingie .
I've suggested the approach to my girlfriend's A460 but she's not thrilled.
The user posted pictures of the process, pictures underwater and even an underwater video. If you have the means and the guts to try out the method please post your results.
Looking forward to hearing from you
EDIT: I found it: DIY - the cheap yet shamefull underwater camera housing | DIYPhotography.net