Open External Links in New Window, compatible with http and https locally

Afternoon everyone.

I'm trying to find a plugin that opens external links in a new tab/window (I know it's not the most user friendly way of doing things but it's required).

However, because our site is a combination of internal links that use http and https I have been unable to find a plugin that copes with all the internal links. They seem to work purely with whatever the current page is loaded as and class everything else as external.

Has anyone found a way of dealing with this issue?

Cheers.

Martin