How to define workflow participant from document attribute

Anybody have any insight as to how to define a Workflow Activity Participant from a WTDocument soft-type attribute?

     i.e. if the WTDocument creator enters in the full name or username of a user into the attribute field, then a subsequent workflow activity will assign the task to the designated user.

We have WTDocument sub-type that kicks off a workflow, but we currently have to use a 'Edit and Submit' task so that the initiator can designate a different user for a particular role later in the workflow (Setup Participants from a Resource Pool). There is a request to eliminate that initial task and jump straight into the main body of the process.

Thanks,

- Jeff