how to get Clocking/Doorways via .htaccess

Hello
i need Help ^^

how to clockaing with .htaccess

(Script-redirect with a filter only with a search engine reffer. (i.e. a redirect only if you go to the site from a search engine) White list of search engines in the variable $ white_engine_search)

Two of my competitors using this method of cloaking.
Interested as well.

This is better done in PHP IMO.