When you use the api, yes it is impossible. What about adding another method called 'Generic Embed', where the user adds the embed code, title, and description to a form, and just submits the form through HTMLPurifier? It would give people a way to add videos from any site to their video pages. I know it's not as robust as using an api, but it's something. There's been a lot of interest in something like this..... might be a good mod for someone to develop.