How can I automatically select the workflow executioner as an Alert's assignee?

I am currently trying to set up an Alert activity that automatically picks up the operator that has executed the workflow and selects him as assignee of the Alert.

The problem I am facing is that the Alert doesn't recognise any JS variable or instance variable (error: parameter not defined in the current context) , same happens with instance.currentOperator.name . 

Do you know how could I could set this up in order to make it work? Any workarounds? It would also be OK for me to select the creator of the workflow instead of the executioner. 

Thanks for the help!