Alone in the dark, I present you Pitfdll, which is a GStreamer plugin for Win32 DLL loading. I guess I changed mind - I don't see a working free software WMV9/QDM2 decoder coming up anytime soon, no matter how close the ffmpeg people claim to be or how hard Fluendo is trying to release binary-only plugins. So we'll have to come up with something else for the time being. The plugin reads WMV9, IV50 and QDM2. More can be added by adding two lines of code defining the DLL and the format it supports in GStreamer notation.
The rushers will notice that it doesn't work in Totem, which is on purpose; Totem is heavily threaded, and threading breaks the DLL directly (see README). I'm unsure why, and would love to get some help from someone familiar with Wine or Xine (the DLL loading code is a direct cp -a from the Xine tree) code in this process (contact me on IRC in #gnome-hackers). Once that's fixed, I'll do a real release and add it to the repositories so people using Totem-GStreamer can finally enjoy those dreaded Apple.com trailers. :-).