How Do I Create This Rewrite Rule?

I was wondering how I could redirect ALL of the links to tag pages on my wordpress MU site that appear on a sub-blog to the clone tage page that appears on the main blog.

In essence here is what I want to happen:

301 redirect http://watches.mydomain.com/tag/gold-watches/

…to…

http://mydomain.com/tag/gold-watches/

I need it to happen automatically as well without going into the backend of the “watches” sub-blog and creating a redirect manually from that sub-blog to the main blog.

Any help is appreciated.