Programmatically assign a task participant

I am trying to set up a participant for a task based on a workflow variable.  I have created a wt.project.role variable that I a setting at the start of activity or the end of the previous activity.  The Role is getting populated correctly, however there is no user getting resolved to this role from the team and so the task goes to the author.

Is there a way to do this?  WC 10.0