Delayed IDoc acknowledgement

Here's the scenario:

1. Send IDoc to middleware

2. Middleware updates an external application database

3. If the database update is successful

4. Send acknowledgement back to SAP

5. IDoc status is updated (possibly status 41?)

Is this possible?

Middleware is WebSphere which is SAP certified and obviously has adapters.

If this is possible, does anyone know what BAPI would need to be called by the middleware or any other way this could be accomplished? web service?

Thanks

Nic