Imported web archives and the OriginalURL metadata: can I set it manually?

When I use the “Import Web Page” feature in Scrivener, it creates a “web archive” file, and also sets the BinderItem/MediaSettings/OriginalURL metadata in the binder XML. This causes the original URL to appear as a link in the footer when viewing the saved web page.

However, I prefer to use Safari to create a webarchive, because I can use the Safari developer tools to strip out irrelevant parts of the page before saving it. I can then drag-and-drop this webarchive file into the binder, but if there’s a way to configure the original URL for the webarchive, I haven’t yet found it. Of course I can add it manually by editing the binder XML, but I’d much prefer some way to do it within the app itself.

Is it possible? Or is this just a really unusual thing to ask for?