We developed an in house "Self Service Delegation" item and process some years ago. Basically you register the delegation (temporary or permanent) and appropriate times. The scheduler runs every 15 mins and looks for any tasks that have been activated for SSD people and re-assigns the tasks to the delegate. After the SSD expires it will swap any delegated tasks back to the original user. It's not perfect but works well for temporary delegations. Permanent ones can become a problem when A -> B -> C ->D because we don't ever clear the delegations out properly.