I added a V-Select pin header.  With a two pin jumper, you can select where the power to the 5V regulator is sourced.  If you have enough voltage (>7vdc) going to the motor, you can use that voltage to power the regulator.  If you have a smaller motor voltage, you can get the regulator source power from the Vin pin of the shield.  You would then need a DC supply connected to the Arduino board.