I think you are looking at creating either a custom DSC or writting the logic in script component.
The LiveCycle api references given in this thread will help you to write this logic.
When the task is assigned to a user you should only complete it with the custom dsc or script. LiveCycle SDK help has examples that will give you a good start point.
When you'll complete the task the process will move to next step in process. You will not need to worry about which user has that taks as the API call will complete the task as System user and the task will get removed from user's queue and next process logic will get executed.