This is feasible within eZ publish, we actually use this kind of "application" in a few of our sites (non-public).
The clue is to use the personlist datatype from us, look in the contributions and
http://pubsvn.ez.no/community/trunk/extension/personlist for the most recent version
It is not optimal, as it should be an object relation list (so to benifit from all obj relation features). But that may be the case for a future version ... we need that ourselves
