Well, whaddaya know, in a stroke of genius I figured out a way to do it with nothing but CSS and png files =)
1. First I made a 6000 px tall top left rounded corner png file (in under 1200 bytes) and applied it to the sidebar left side.
2. Then I rounded the right top and bottom corners using CSS and added hex color fill for the rest.
3. Finally, the bottom left corner was rounded using a png image placed in a footer (pushed it outside of the footer using CSS - It loads on pages without a sidebar, but since it's white on white it's not visible)
4. Outer rounded corner was set as a background of %bar2
That left me with opportunity to style widgets independently.
Damn, I love a good CSS puzzle!