There's two ways of doing this that I've found so far. One is:
REG_PIOD_OWER= 0xff; // you only need to do this once
REG_PIOD_ODSR = data;
Output is all over the place though - pins 25,26,27,28,14,15,29,11 (I think). Take a look at Graynomad's Due pinout diagram to see exactly where (Port D pins 0-7)
The other way is more convenient for wiring and the code is only slightly more complicated:
REG_PIOC_OWER= 0x3fc; // again you should only need this once
REG_PIOC_ODSR = data << 2;
and the pins are 34,35,36,37,38,39,40,41 which are all nicely together on the bottom connector.