AFAIK, it’s not possible and there’s not even a good concept in XMPP.
With XEP-0066 you would upload the file somewhere to an external File/HTTP Server and then send the URL of the file to the MUC room. Each MUC occupant could then download the file.
But it’s of course a different approach as opposed to the “file streaming” in 1-to-1 file transfers.