not really any solution, it's worst because advertisers bid less for that size ads in general.
you could however get that ad unit additional eyeball time if you place navigational menus adjacent to that unit. But that eats into your useable content areas.
but if you have that much space to either side of your page, a 300x250 usually performs better. I assume you use those units as pure display and not going for targeted text in-content.
I would personally combine the use of 300 x 250 + leaderboard banner + 160 x 600 to get the most of bids for each individual sizes, placed on your most visible locations to garner the most attention and potential clicks.
Depends on the day, oddly enough. I've seen days where the bottom one kicks ass and then vice versa. So I leave them both there and it works out fine. There's no way to predict which will do better on a consistent basis.
Just put one before the content at the top of the article column, and one after it right after the content ends. If you need to then make your article column wide enough to fit the 728x90 right over the title of the article. Don't put it way at the top of your blog, it should appear right in the article column itself.