As Robin says, that function does not exist for VASL.
Many people have asked for it over the years, but as I understand it, quite a significant technical problem stands in the way. I can't remember what it was but I seem to recall it was something as fundamental as 'Well, then we would have to redo ALL the counters' or some such. In other words an epic sh*tload of work. But I might be mistaken with regard to the details.
von Marwitz