Assign to first or last assignee workflow post-function

Within a workflow it is possible to assign an issue to a particular user (person), by specifying a Post Function 'Update Issue Field' for the 'Assign To' field, or by using the Post Function 'Assign to Reporter'. What is missing is a means to (re)assign the issue automatically.

Consider the workflow we need in our organisation:

1) Create Issue
2) Open
3) Resolve (Incomplete)

• Assign To Reporter
  4) Reopen Issue / Clarified
• Assign to Original Assignee / Assign Automatic
  5) Open
  ....

The issue is opened normally. In step 3 the assignee discovers that the issue is incomplete, and Resolves the bug as Inclomplete. Now, the Post Function 'Assign to Reporter' takes care of assigning the bug to the reporter. The Reporter should now be able to add information that will make the issue complete, and Reopen the bug (or use some custom WF action, e.g. 'Clarified'). This should assign the issue to the orginal assignee automatically (throug a Post Function).

The reason this functionality is needed is that we do not want to give all reporters full assign rights, but want to be able to return an issue to a reporter.

A new Post Function should be implemented that is equivalent to the Automatic assign that is used when an issue is created, or a fucntion that assigns it to the previous assignee (the one that sent it back to the reporter, in our example)