I have two of the injectors (I bought one and then my wife bought one as a gift for me a few weeks later). It would work fine for your application. You would use the whole cartridge: hit it with a burst, purge, hit it again, etc., until it's used up (it won't take long, 4-5 bursts). Don't just lay on the trigger and try to empty the whole thing at once, and don't pull the trigger without the disconnect on the keg, and you won't have any trouble with the thing. At all.
That being said, I agree with some of the others. I believe you're overthinking it: rack to the keg and go about your way. Unless the keg is less than half full, I can't imagine you having a problem with oxidation.