Printing plates larger than 11x17 on a hp 5000n

[crcprint]

I am trying to print a 12x193/8 plate on a hp 5000n, to run a 11x17 job. The problem is the printer only let me print the image in a 11x17 area. In other words I the image is about a 1/4 inch from the top of the plate, and it needs to be moved down to about 1 1/2.To allow for gripper room. I am printing from a MAC os9 computer. Anyone know how to make the image move down and sill have all the image on the plate?

Thanks Darryl