If you watch the videos at the link I posted you'll see that my car is a WRX RA :-)
Sadly there does not seem to be any reference to a 5th injector in the ROM. The difference between the WRX and WRX RA ROM is only the rev limit. The 5th injector is one of those cool things that people brag about but actually never use.
At the moment nothing is switchable, there's basically no free space left to evaluate a switch input. In future I might hardcode one value for a map like the boost control map and use that space, but that will be if I ever decide to add NLTS.
I'm not sure how much fuel anti lag will use but I think it'll probably be worth all the fun from scaring other drivers off the road, lol.