Kjay:
There may be some severe debate over the gramatics of this...." "only one feeder or branch circuit that originates at the additional building or other structure to supply power back to the original building or structure unless permitted in 225.30[A] Special Conditions."
"Only one feeder or branch circuit...." 'only one....or...' . Reading the OPs comments, there seems to be a 'feeder' and a 'branch circuit' involved in his scenario. Now, the 'branch circuit' is a 3-way switch loop, with the 'load' at the outbuilding. Assume the 3-way circuitry contains the neutral for the 'load' (hopefully, as this was not mentioned), so the switch loop can be defined loosely as a branch circuit. That may be construed by some as there is both a feeder and branch circuit, and be an issue.
George, what say you of the above??
