Would it be possible to add a parameter like the "streaming" config option that was mindlessly obeyed by webviewer? Webviewer's "does HTTP range work?" check is run against the server hosting the WebViewer JS files, not the XOD document itself. At present I can set streaming:false, and WebViewer will perform a test against the server it's javascript is loaded from, and end up running in streaming mode anyway.
If you wanted to avoid support calls you could always give it a name like "dangerouslyForceStreamingToOff" or similar :-)
Regards
Donald