[Plugin: WordPress MU Domain Mapping] Redirects issue

I installed the domain and put in all the usual records etc and the domain points to the correct sub domain, i then enabled the donncha plugin and it maps the correct blog…. however I have had to do a redirect to stop the subdomain from being picked up by search engines… the redirect works great for top level but not when there is a post in the url using permalinks….

what I need is for http://sub.domain.com/posturl to be redirecting to http://domain.com/posturl permanently…

I have the top level all working just not the permalink version and both urls work if I manually type them both so its a simple issue, any help appreciated….. maybe a feature request for the next update on subdomain mapping…