workflow modeler - assign task to specific user mid workflow?

System

our consultants tell us that with the new workflow modeller it is possible to only assign a task to a specific user on workflow instantiation, not mid workflow.

i.e., we want a reviewer to be able to select a specific person mid workflow (from a dropdown, picklist, etc) to assign for a secondary review. we are being told that with the workflow modeller this can only be assigned to a group, not a specific person. any help/advice would be appreciate, cheers