Injecting that much air would send your AFR's a bit mental, plus you have to match that with fuel and it won't actually spool the turbo instantly
EDIT: actually thinking about this. If you inject air after the turbo it may want to turn the turbo backwards (maybe), and if it is injected before turbo, your gonna lose most of it out of the filter
Holset (from memory) were researching and developing an "E-Boost" that used a small electric motor to help the turbo accelerate from low RPM or something like that. Saw this a while ago so don't remember much but this is a much better idea. Still I can't really justify it on an RB. As had been said. You would lose alot of the energy ou are "gaining" with powering whatever you end up using
A KERS type system is what I'd have to say would be the closest to using an energy sorce to help acceleration, but the weight/complexity of such a unit on an older car would make it kinda useless, especially when you have to recharge it. On new cars where it can be built in, yeah but I sorta don't see the point unless it's used for taking off/getting up to speed rather then an actual speed boost