AOLServer 2.3.3 used to do just what Rafael wanted. Sometimes there is still support for old features even if they are not mentioned in the docs for the 3.x versions. Try:
[ns/server/yourservername]
UserMapDir=public_html
Or a suitable equivalent if you are using .tcl style initialization files. It may not work but the worst it should do is ignore you if the feature is not supported any more.
