Prevent missing links through mandatory link in some process steps in a workitem

Hi,

are there any workarounds or methods which prevent users to save a work item if there is no link to another work item?
For example in our work item work flow there should be definitely a Contributes To Link to a Change Request from a Story if the Story is going to be closed. Otherwise the user should be blocked to save and get a error message ("missing "contributes to" link").

Please tell me if there is any solution available or any workaround which prevents some misusing.
Reason for mandatory links are the plan view, which doesn't work any more correctly if there are links missing.

Cheers David