Roles and Priviliges Question

I am looking for a way to tighten security on our databases by defining roles so that users from a certain group can only access particular tables with pre-defined read and update priviliges. Usage of the informix roles utility appeared to be the answer, allowing associating of a new user particular role definition. Unfortunately, it seems that this only takes affect when the user issues the set role command for that session. Is there a way of making roles more permanent, and initiated without user intervention Thanks Paul