I found out that I needed three little helpers to get the most out of the CNC.
 
Quickly I realised that the method of setting the z height by hand, as well as the positioning of the block (double sided machining for first CNC project is keen.) by eye just isn't going to be good enough. Since its not my CNC machine just to hack an automated touch block onto, I had to do a low tech solution.

It took all of about 30 minutes to design and cutout a tiny corner block from MDF and cover it in tin foil. This I can slide onto the bottom left corner of the stock, and with a multimeter set to continuity testing, slowly jog the end mill into position. Having measured the block with calipers beforehand, its simple to define the offset to the corner of the stock. Each axis is 'homed' using this and G92 commands. Its not perfect, but its good enough.  

The second helper is just some mounting blocks for the initial drilling. The mounting solution is to drill out a 75x75mm M5 bolt pattern to match the X-Carves wasteboard, but since I use the CNC to do this, the initial stock needs to be mounted first. This is nothing more than a fixed corner piece and some sliding adjustable ones to lock the stock into place.  

The last helper is a waste board with the M5 holes drilled out so it just acts as a cover for the x-carve. Nothing fancy about it at all.

All three items were super quick to model and cut, and hopefully will last a lot longer than this project!