Literal “space filler” sidebar plugin/widget?

I would like to have something in my sidebar that adds additional content to pages that have room for it (i.e. where the main content runs longer vertically than the sidebar content) but does not if the sidebar is already the determining factor in the length of the page. (I’m talking about a basic Kubrick-style layout.)

For example, on the main page of my blog the list of the most recent 10 posts always runs longer than the content of the sidebar. In this case, I wouldn’t mind having the sidebar filled in with some Flickr thumbnails or links/descriptions pulled from one of my delicious tags.
However, on most individual post pages, the sidebar already runs longer than the post, and adding anything to it would just worsen what is already an off-balance layout.

Does anyone know of any plugins/widgets that are ‘smart’ enough to judge the distance between themselves and the bottom of the page and only add more content when it’ll actually be beneficial rather than just obnoxious?