I wish to have the ErrorDocument set to the domain being used..

I have a UK and USA version of my site with slightly different content depending on the site being viewed. But as I have it now...

ErrorDocument 404 http://www.mysite.com/errorpage.php

if an error page is found using the .co.uk site the visitor will always be taken to the .com sites error page and not the .co.uk sites error page.

How can I have it so it will take the visitor to the correct sites error page for the TDL they are viewing it by?