You could upload the videos to another video hosting service instead of as a container (IE vimeo), then embed that to a webviewer by URL stored with the FileMaker record.
Also, have you tried other formats? I'd imagine with how WD functions, the behavior you have noticed (full load before playback) is consistent across all formats, but I have not played around with this too much.
That's exactly what I am trying to do. The content streaming is working randomly on various situation.
I'm checking if this is related to the firewall and content type.