Clear out no longer existing users

Hello Everybody,

as a educational institution our user management is done by various tools. But all of them just alter eDirectory and so after the (school) year is over all users that left the Institution are removed from eDirectory and so LDAP. But now groupwise keeps the users accounts in the groupwise System.
Well it might now be possible to connect the old accounts to new eDirectory users but I´m lloking for a possibility to get rid of groupwise users no longer existing in eDirectory/LDAP. Is there an easy way to do so or do I have to take a look at every user to find out if he is still in the System and if can Keep him or not?

System is an OES11 Server with GroupWise 2014 SP1HP1 planing to update to GW2014R2 soon.

Haven´t found anything about it in the documentation or the forums so any help or advice is greatly appreciated :)