Shared Workarea Locking Issues

System

Is there any way to automatically run an External task after a user takes ownership of a Group task? Here's why I ask, and let me know if I'm heading completely in the wrong direction:

Everyone is using the same Workarea. Here's the basic workflow:

Content Provider -> Manager(s) -> Review Committee -> Staging

After the Content Provider starts the workflow and submits their file(s), they are sent to the Managers which is a Readonly Group task. After the Manager reviews and approves the content, it's sent to the non-Readonly Review Committee Group task.

So, what keeps the original Content Provider from editing the files as they go through the workflow? After person in the Manager group takes ownership of the Group task, shouldn't the file(s) be locked by that person so the original author can't edit them anymore? There is no way to know who the Manager will be before they take ownership of the Group task, and there is no way (that I know of) to automatically call an external task to reset the locks to the new owner when they take ownership. The same thing will happen in the Review Committee task.

Here are the two solutions we've come up with so far:

1) There could be two Workareas - One for Content Providers and Managers, the other for the Review Committee. After the Content Provider submits the files to the Managers, relock them as a "dummy" user. The Managers won't be able to edit (which is fine since it's a Readonly task anyways), and the Content Providers won't be able to either. After the Manager approves, the files get submitted to Staging, and then get sent to the Review Committee, who can then edit them in their own Workarea.

2) After a person in either one of the Group tasks takes ownership of the task, make them complete another task that locks the file(s) as themselves. This is not preferred.

Does anyone have any other suggestions and/or comments?

TIA,
Ronnie