Turning Posts Into External Links

Is there a plugin or something to allow posts (when previewed from the homepage or category page) to link to an external website as opposed to taking you to your own article page? Each post would also be linking to a different URL, so there’d have to be a feature in the AdminCP asking for an optional URL to override the default.

I’ve seen it done before, but I know next to nothing about coding… so I was wondering if there is some kind of pre-existing (i.e. easy) way of achieving this. I just need pointing in the right direction.

Alternatively, if anybody could lend me a hand with coding this crap, I’d be more than willing to pay. 🙂