Adding "now playing" title metadata to an asf stream, how?

[isync]

This forum post expects vlc to be able to pass dynamic environment variables to the streamout via variables, e.g. --marq-marquee="$N".

Now, is it possible to do the same for ASF? Adding --sout-asf-title "Now playing: $N" to a vlc command does not work, the $N gets replaced by <nothing>.
And where is the list of available variables, like $N, $L, etc.?