Using Excerpt for Header Information (or any equivalent)

I know the_excerpt() must be called within the loop, but is there any possible way to utilize the excerpt portion of a wordpress entry for a meta description tag (sort of <meta content="<?php the_excerpt(); ?>" name="description">)?

Essentially, I’m looking for a way to change the meta description tag for each individual post. I have yet to find a plugin that will do this, easily, and using the excerpt field seems perfect, if there’s a way to do it.

Could I call the loop to get the excerpt within the header, and then rewind_posts() and call the loop again to display the post?