Forcing a redirect from HTTPS to HTTP for one controller

Hi
I've implemented my CodeIgniter 2.x site on a server with SSL and have included a .htaccess file with all the relevant redirects to force HTTPS. However, I need one part of my site to remain HTTP and I'm struggling with this because of the way CodeIgniter processes requests through the index.php file. I want to keep mydomain.com/cron as HTTP and cron is of course a controller processed in the same way as all other controllers. So far, my .htaccess file looks like this:-

Thanks