I could use some help on a layout. This is what I'm trying to achieve:

Here are the specs:
- header has fixed height
- footer is always at the bottom and has full width (100%)
- content has fixed width
- content basically has full height minus the footer, but overlaps the footer by exactly 20px
This of course must work when the content is both shorter and longer than the viewport. I've been playing around with this for a few hours and I just can't get it to fulfill all the features.
I created a fiddle for it here: http://jsfiddle.net/Sq4Pk/6/
The problems with this solution are currently:
- the shorter the viewport gets, the more the content overlaps the footer (must be exactly 20px)
- the content part does not fill the viewport
Is this even possible? Can somebody help me out with this?
I've tried these solutions and variations thereof but both are slightly different from my usecase:
Thanks a lot for any help!
Chris