Multiple Websites Reference External CSS Files

I am running multiple websites that are identical in look and function, and only their content is different. Currently I have the option of running the same stylesheets across all the sites simply by maintaining each every stylesheet on each website. Of course, this is very tedious and time consuming.

How can I setup multiple websites to access the same stylesheets and javascripts from one common external server?

Here’s the trouble … I know I can simply access the external CSS and JS with a protocol-agnostic link, but how do I designate each individual server for a given image or content link?

Take this background image for example. In it’s current form, it’s going to try and pull up the image on the server it’s residing on, which is an external CDN server.

.custom-checkbox label { background:url(images/styled_checkbox.png) no-repeat; }

Of course, there’s no image here.

What I need it do is this:

.custom-checkbox label { background:url(//server-requesting-image/images/styled_checkbox.png) no-repeat; }

These calls will come from multiple servers. So I need an array of servers it can reference. Please let me know if there’s a WP script I can use, or maybe a regex in a server conf file.

Please let me know if you have any questions. Thank you, Tom