Well, if I remember correctly, that box of bioballs lifts out right? I would put the macroalgae on that side, and put a piece of eggcrate (light diffuser) in between the baffles to keep the macro algae from floating through to the other side where the pump goes.
Then you could hang a small light from the bottom of your stand to light the side with the macros.
You might want to raise the divider between the two sides or your refugium isn't going to be very deep. I just glued in a piece of acrylic (on the right side divider in your picture). Just make sure you still have enough space to hold the water that will drain down from the tank if the power stops.
