Probably a better question for Paul, but am I missing something?
Let's say he has example.com, example.org and example.co.uk. If he wants people to go to either of these domains and the page rendered is the homepage for that domain, ie that domain is exactly what is in the address bar, then how can this be done with 1 WordPress install? A single WP install can only work with a single domain. Changing the domain breaks the WP structure.
I hope I'm wrong mind, because this would seriously help us with a project we're working on at the minute
But what you suggest tifosi, in my mind, only works if the original domain forwards to a single central domain with the WP install. Now this could be what Paul wants and I've misunderstood, but my impression was that the domain wouldn't forward, it would instead render the instance of WP as its own site defined by the fact the domain doesn't change in any way.
I can only see this working as either some parameter or sub directory that defines the domain following a redirect, or by multisite where one WP install allows multiple domains to render on a single install.