The only way you'd normally do broaching under CNC control is using a rotary broach (google it!), where you plunge an offset/wobbling cutter into the workpiece and the wobbling action cuts/shears it's way into the workpiece.

Conventional broaching isn't really suited to CNC, as it normally involves using a guide bush to guide a broach cutter through the material. I'm sure you could automate the process, but rotary broaching is far quicker.