what i am trying to do is create a provisioning request that can be
partly verified by the IDM system before heading to a user.

For example, a user wants to change an attribute of theirs (i.e
telephone number). They issue a request and the system does a lookup to
check for duplicates before passing the request off to the line manager.

Is it possible to add additional functionality into the provisioning
request such as a java call that can do the lookup to check for
duplicates? If so, any thoughts on how it can be done.

Slowly getting my head around Designer with the provisioning plugins and
this is hurting my head!