You can wire it for as many batteries as you like - just make a Y harness in the plugs, similar to this:
With the warriors cables where the female plug is on the picture.
Installing a UBEC is simple, remove the black jumper from the warrior, solder up the UBEC's power leads to somewhere on the battery leads, and plug it into the power port on the reciever. Just done.
Welcome to the forum btw mate.