Unfortunately that wouldn't be very possible, seeing as $sound() only seems to take information about the file via the mp3 header/id3 tag. $insong does have a .pos property though... if that's what you're looking for.
I _did_ notice a .vbr property for $sound() while looking through the help.. You could use that to test if the file is VBR, and if so, ignore $sound()'s length approximation..
