Secure Submission (HTTPS) of Forms using Contact Form 7

I want to make submitting forms using Contact Form 7 secure (e.g., using HTTPS instead of HTTP), but cannot figure out how to do so. The only posting I found was old and not useful. I don’t want my entire site to be HTTPS, just the submission of the form.

Thanks in advance for any guidance.
michael

http://wordpress.org/plugins/contact-form-7/