[wp-hackers] Correct way of adding author to Custom Post Slug

[Robert Lusby]

I'm trying to setup the default Permalink Sturcture for a Custom post 
type to match as the following:

/custompost/%category%/%author%/post-name

And I'm at a complete loss on how to do it...

I tried 'rewrite' => array('slug' => custompost/%author%') in 
register_post_type, and then some filtering on post_type_link to replace 
%author%, but that doesn't help with category.

It also doesn't work when loading an archive page:
http://example.com/custompost/category -> 404
http://example.com/custompost/category/author -> Loads, but informs me 
that no results were found for the requested archive, even though there are.

I'm sure this shouldn't be this complicated so what am I missing?

Thanks in advance.

Rob.