Hi Michaela,
Create a UI task say "Copy BUsiness Role" which has provision to give the new business role name and another filed to select the reference role Z_refrole.
Under that task, add a to Identity Store attribute as shown below.
For the MXMEMBER_MX_PRIVILEGE attribute, you have to assigne the privilegs of the reference business role.
So, in the value field provide {A}Z_sap_getprivilesofroles(%Z_refrole%)
Inside the script, get the MSKEY of the referenced role and get the associated privilges from the idmv views
Thats it. Your job is done.
All the best !!
~ Krishna.