That I know of there is no “free” option to setup an automatic webinar that looks like a real live one. There is a plugin that will simulate this pretty well.
You can find the details here http://coachlikes.com/autowebinar The best free way I can think of is to setup a landing page with an optin, then have it redirect to the youtube video, or self hosted video on a WordPress domain you own.
But I would HIGHLY suggest you at least try a few live first. Just to get the feel of it. Nothing will ever convert better than live. With the video there is no user engagement.
You can answer questions etc. PLEASE give it a try. If you already have the videos done, then the content will be easy. Just repeat it .. only do it live. If not, try the link above. Let me know what kind of results you get either way. Would be great for us all to learn from.