[TEMPLATE] Left sidebar on index.php only?

I’m trying to put together a blog where there’s 2 sidebars (one on each side of the content column), but only for the index.php page. For the other pages, I want the left bar to disappear and for the content column to expand into that space. Sort of like at Under the Radar (if you click on the single post). Does anyone know how to do that? Or is there a naked theme that does that which I can customize? Thanks!