This feature has been added to Tiki6
When the site is accessed through specific domain names, redirect to an alternate domain preserving the URL. Useful for domain name transitions, like tikiwiki.org to tiki.org.
In tiki-admin.php, search for "Domain redirects"
The redirect is for domain only and should be put in this format:
Note: One entry per line. Comma separated list: old, new
As explained at http://dev.tiki.org/wish3164