Superorb, that's a tough situation. Have you tried using a fan (box fan, or something that you can control a tilted angle, not a tower fan) to help funnel cool air up your stairway? I'd also recommend getting awnings to place over your windows that get full sun, and get some heavy-duty insulation-lined drapes for the inside of those windows. The drapes will help keep the sun out in summertime, and will help keep cold out in the winter. Multi-pronged approach on that problem....