Instead of piggy-backing audio cable on the video line drops, can the video lines be installed with 50 Ohm cable as well? Then you can drop antennae near the camera rigs. I would assume you would need an amplifier (Lectro UFM230?) on each run to compensate for the longest distances. At 50,000 square feet, if your stage is a square, then you're talking about 225 ft. by 225 ft. (The longest run at the diagonal would be 316 ft.) Depending on where you are and what kind of RF is in your area, this might be doable. Here in NY, with so much RF, that distance would really start to stretch the reliability of that setup - and probably wouldn't work.
Josh