SlamTex
I believe you are mistaken about not "driving a ground rod" when you bring an Equipment Grounding Conductor with the conductors supplying the building. If there is more than one branch circuit to or in the structure you must bond the panel or disconnect enclosure to a Grounding Electrode. That electrode could be any of the ones in 250-50. If you ran an Equipment Grounding Conductor with the supply circuit/s you do not bond the grounded conductor to the enclosure. If there are no metallic pathways of any kind between the buildings you could omit the Equipment Grounding Conductor from the supply circuits or feeder and bond the grounded conductor to the enclosure.
