Keeping a decent frame rate? Then, my tweak isn't for you. It's for people that want to have as large a FoV as possible while having the highest possible resolution and aren't bothered by the significantly lower framerate. (Of course, its low-light performance, because of full oversampling, is far superior to the stock 1080p mode.)
Unfortunately, all you can do is switching to a much less resolution. If you use the stock 640*480 resolution (accessible via both third-party AppStore apps and CameraTweak; I'd go for the latter), the low-light performance will be significantly better than using the stock 1080p / 720p modes.
I'll also play a bit with binned mode, which did work on the 4S in 720p (I've even published an article on it) and delivered superior low-light performance (on the expense of the resolution). It's only available (if it is) on JB'n iPhone 5's. I'll report back.