I don't know the answer either. But here's a SWAG:
I think I would just fertilize with any good, balanced organic fertilizer such as Mills Magic or Espoma. If you don't prune the rose severely each year, it's need for nitrogen will not be very great, so a little loss to the grass should not be a problem. I assume that when you mow, you mulch the grass in place. If so, that returns many of the nutrients into the ground, anyway. Maybe grow some low-growing clover in your sod, and the nitrogen problem is solved.
