The purpose of the electrical box is two fold. One is to hang and support the fan, the other is a safe place to make electrical connections.
You are way over engineering the hanging part, while not paying attention to the safe connection and wiring part. Whatever method you use to anchor the fan, you still need an approved enclosure (box) to make electrical connections. And a secure way to get the wire there. Your proposal of an extension cord is probably not a good idea.
You are way over engineering the hanging part, while not paying attention to the safe connection and wiring part. Whatever method you use to anchor the fan, you still need an approved enclosure (box) to make electrical connections. And a secure way to get the wire there. Your proposal of an extension cord is probably not a good idea.