play display from MacBook to projector connected to mac pro
Install software like Reflector 2 on the Mac Pro.

Then your MacBook (assuming it can airplay to other displays) will see the Reflector advertisement and push the MacBook screen to the window on the Mac Pro.

Once that's set - set the Mac Pro to direct the Reflector 2 window to full screen on the projector.

Worst case, you'd need software like AirParrot on the MacBook if it's not new enough to AirPlay to a remote screen from the OS level and hardware.