Yeah. So I finally fixed my portfolio. Thanks to GK and everybody else who pitched in. I found a great resource here (thanks to Sour Bob for sending me there), as well.
Sometimes it’s right in front of us. The solution, from a very nice person on the css-discuss list, was this:
Use a background image in the centered container the same width of the right column, placed right, repeated vertically.
Duh.
In my case, that would be not the big container, but the one I use to hold both the main content area and the sidebar.
It works in both these conditions:
It really works. Crisis. Averted.