As far as I know, in Sitefinity, SSL is an all or nothing deal. If you enable it then it will redirect to https each time the page is requested. If it's not enabled then any attempt to browse via https will redirect to http.
I'm curious, if you're going through the trouble to purchase an SSL certificate and enable it on a page then it must contain something you would like to transmit via secure communication. May I ask why, then, would you want it accessible via http?