using disable_functions silently

I would like to know, if there is any way, to use disable_functions silently. We are running an shared hosting environment and therefore forbid the use of exec() etc. Many of our users, just seem to be to dumb to comment out exec() in phpBB etc. Since removing the exec()-calls works fine, is there any way to just omit them silently from the server side? This would be extremely helpful for us, our support and our users! Regards, Samy