Outlook Update List

I'm a software developer and my project consultants delegate development tasks through Outlook's Tasks pane. It works pretty well:

- Bug is discovered
- Consultant creates a new task in Outlook and assigns it to me.
- Any updates or completion status is reported to the consultant.

Works great. My question is, how do I include the consultant(s) in tasks I've created for myself? When I go to details there's an Update List field but I can't enter anything into it. There's an "Unassigned Copy" button that seems it might do the job but it's greyed as well.

How would I put someone on the update list for a task I've created for myself?