This addin for Nintex Workflow 2010 adds the ability to choose a user or group when an 'Assign a flexi task', ‘Request approval’ or ‘Request review’ task is responded to. An extra panel with a people editor input is displayed on the task form. When the task is submitted, the selected people editor value is stored into a nominated list item property. The workflow can then read the value from this property.
Please refer to the Nintex Workflow 2010 SDK for more information, specifically "How to > Create a custom task form".
UPDATED: 28 Oct 2011.