Workflow Releasing Parked Document - Agent finding problem

Hello together,

i set up a workflow for releasing parked document within the standard customizing of SAP (OBWE) using the subworkflow WS20000045 (Amount Release with User Decision)

But the problem is: finding the right agent.

When i declare the role 139 as a general task, everybody gets the workflow in the inbox.

I want to assign a special person according to the reference in the parked document. (for example: reference is : 99999999 then agent is mr.smith//1111111 then agent is mr.schneider)

do u know a user exit or any other hint which can help me solve this problem.

Thanks in advance.