Aaron B is probably on the right track. How long is the section you actually want to carve? If it is less than 144", then you can design on a board of the size of the area you wish to carve and then either center it or jog it into position. There are currently some limits in the firmware that will probably not allow you to center on length, but you may be okay with jogging into position.
If the azek is expensive, I recommend testing this on something cheap. We have not really tested with anything longer than 8', so this is unexplored territory. I do have an item on my list to review the distance limits on the X (length) axis. This is not at the top of my list, but let me know if you have any problems, and I will see about making this a higher priority so that I can get you something that works.
Chris Morlier
CarveWright