There are other audience recording out there, if I remember correctly. Can't those be used to fill in the gaps? Might even be worth a shot to create a combination of all the audience recordings, picking the biggest reactions of each one to make one track that's actually more lively...
Format wise, would it be possible to use different recordings for a front/back split? That way it would sound like the audience is actually all around you, and you're sitting amongst them.