Have you considered using post actions to either pull the UATs from the tasks or push the UATs to the task?
This is relatively easy to accomplish if you have some experience of configuring your own workflows. It allows you to generate the tasks required based on the Acceptance Criteria (i.e. each would create a new task) and copy the details of that into the task. I'd focus my investigations around that, as it can be a very powerful tool in your testing arsenal..
I'm afraid I don't have an instance of Jira available to me at the moment or I'd dummy up a workflow for you that could potentially handle this (and any duplication).
I reckon you would need the following:
1) Custom fields for UAT and Acceptance Criteria
2) A workflow step like 'Approve' that generates the tasks and does all the post-function work
3) A filter or two to manage the output and track any unwanted duplication (based on your custom field content matching another custom fields content).
Sorry I can't help you more directly.