Program a little Wordpress plugin -- 3

I am looking for a guy who can program the following simple wordpress plugin: By activating the plugin, I want to have the option to determine for each WP post (so, this function should be placed in the WP post interface) whether an ad code shall be implemented or not. In case the option implement ad code is activated, an ad code predefined in a setting area will be inserted to the wordpress post right after the <--- more ----> tag of the post I WANT TO BE IN NEED TO ADD ADDITIONAL SHORTCODES TO THE POST TEXT TO GET THAT AD CODE IMPLEMENTED - just check the option and its done!