In the past, I have seen someone who created a custom Arducopter firmware with a new WP_YAW_BEHAVIOR to do this. Never tried it as it seems a bit unpractical to have a custom firmware just for this, but if you really need it I think you could look for it.
I could think of another method : change the WP radius (make it small to be sure to stop at the right position), add a delay (1s) and then add a DO_CHANGE_YAW command in your flight plan(angle= angle between this point and next point). This should force your copter to stop, turn, then go.
Hope this helps