Hi MR,
To my knowledge, if the Nurse Practitioner has already been enrolled with Medicare, then he/she would just have to submit 855R (for reassignment of benefits) with the group's name as practice location and pay-to-address. Also, the group's information with PECOS system would need to be changed with the details of the newly added non-physician practitioner.
Now, if the Nurse practitioner is not into Medicare system yet, then he/she needs to submit 855I (individual enrollment application) with the group's name as practice location and pay-to-address and then the PECOS has to be updated with his/her Medicare ID as "PENDING".
Regards
Sriram