I thought about doing pretty much the same thing, although I use a CSMIO-IP/M motion controller with Mach3. I had been squaring the thing manually, which worked OK, but someone usefully pointed out that the CSMIO is a four-axis controller, and it's pretty simple to switch between 4-axis and 3+slave axis configurations. Combinied with a homing macro that homes both X and slave axes simultaneously to stop the thing going out of square, it all works fine. Not sure if there is a workaround like that that you could do with the DDCSV?