this is difficult. You will have to find the points on the pcb and solder wires to them with a SMD soldering tip. The links to Onefinity’s pcb layout gerber files are in this posting.
If I wanted to use this option, I would rather buy the Buildbotics controller right away. It can do everything the Onefinity controller can do, but has new features in its operating software (see here and here) – and the auxiliary 15-pin port.