Download WMV for your client version. Open it. Select path to your WoW. Go to Options menu, select Settings there. Click on Add and add custom MPQ you want to have added into an MPQ list. Do this for every single MPQ, and do this in order in which MPQs should be loaded (so the last will be overwriting MPQs before, like it is done in client, so start with patch A, then B, then C...).
Restart WMV and you are done. This won't work for MPQs without listfile though. If your MPQs don't have a listfile, you'll need to get/create one, or you are basically screwed.
