I would think that this would be no problem. I like your idea about the spare, though I'm not sure if the RIP would configure this without actually moving the physical location of the head or just the "wires" firing it. Since the platform is configurable for 3 and 6 dual channel heads, perhaps if you call them they could do a custom "4 dual". It probably would not be cost effective for the extra expense and the fact that you could not load it fast enough get more shirts per hour.