Its bit long process since I don't know the name of property which will hold the value.
But you can always trace the agent and see the property values which are present just before CreateWorkEmail activity or any of your custom activity is called. Then you can use the property value in while creating the WO.
Thanks for posting the query. PFB information which might be helpful to get the email listener at run-time.
Create a function with paremeters LogAttribute and ListenerAttribute and put this code, from your service activity call this function with param value (Stack,ListenerName) . function will give you the listener name