I am looking for a way to let a customer portal user  trigger a action which assign him to a different profile.

I have tried with, triggers, @future method, time based workflow but these approaches all leads to the

FIELD_INTEGRITY_EXCEPTION, Cannot change profile for current user.

Is it at all possible that a customer portal user activate a profile change for himself? 

I am looking for a way to let a customer portal user  trigger a action which assign him to a different profile.

I have tried with, triggers, @future method, time based workflow but these approaches all leads to the

FIELD_INTEGRITY_EXCEPTION, Cannot change profile for current user.

Is it at all possible that a customer portal user activate a profile change for himself?