For anyone looking for a third party solution for this, please try the following:
- Register for a trial of Project Processes here: http://bit.ly/2xMBkVk
- Create a new process and connect Asana with a Custom Action.
- Complete the Asana authorization process.
- Click on Get Started under Auto Numbering.
- Complete the wizard.
You can setup a prefix for the number, a suffix, a starting offset, etc. We can utilize custom fields or simply prepend the information to the task name which works better for searching or non-premium users. If you have any questions or issues getting going, please send me a message.