I won't say that's impossible, but it's close. Htmlpurifier reads a configuration schema that needs to be recompiled to add the new filters. This requires shell access because you need to be able to run php files from the command line. The way it needs to be done, is add all the filters to the configuration schema, then add an admin interface that allows the admin to choose from which sites embedded videos will be allowed.

It really is about time D7 started taking advantage of the whitelisting see more capabilities of HTMLPurifier. It would be nice to see new filters added with every new release, and now would be a good time to start