Sharing css files across all blogs in multisite

I know this isn’t the true purpose of MS but we’re using MS to create separate sections of our site so most of the site(S) uses similar themes and CSS. I’m wondering if there is a way to share specific CSS files across all sites other than linking with the full URL. For example, our IE specific stylesheets will have the same function on all our sites, instead of updating multiple IE css files for each theme, is it possible to park them someplace and then link from there using something like:

<link rel="stylesheet" type="text/css" media="all" href="<?php bloginfo('template_directory'); ?>/ie8.css" />

Or should I use the full URL in the header file of each theme? Right now we have about 12 sites and going through and updating all of those with the IE specific CSS is a pain.

I’d love to be able to do this with my footer and header files as well (if possible and easy).

TIA!