We currently use HP Service manager for trouble tickets, but also for requests. Developers basically send a request to our Command Center, and they work the request. This offers a certain amount of tracability.
If you're just looking for basic workflow, you could leverage something like SharePoint (just do a 3 step flow - Submit, approve, work).
Additionally, you may want to think about what you would like to happen if and when the ADHOC fails.
Finally, if you're using ESP, they are working on a Self-Service portal of sorts. However, RickR has written a PHP based system that uses ESPImi.
Hope this helps.