Well, I was being stupid enough not to have read your post properly in the first place, but hey - glad you fixed it!
A test on my system appears (I haven't fully proven it) to show that the web plugin follows VLC's options, but I'm not 100% about that. Alternatively, you may be able to use the vlc plugin's API to write a small bit of javascript to switch track or disable subtitles: either run from a file or directly in the address bar.
Or just open VLC as an external player, of course :)