Hmm...I did a test with an exported set of files from camtasia and the FLV method they use seems to work fine as a placeholder in XWD for me. In their case, they are using a small "controller.swf" to load up the flv file. The html part of things only has the call to the controller.swf.

I'm not sure what the basis of these files are, but they do work in XWD here, so at least I know it can be done. I'm not sure, however, what is in that compiled controller.swf.