I just used 4 SWUs on HND-LAX next summer. One AAgent I talked to told me sorry, you can only use up to 2 SWUs at once, for yourself and a companion.
I'm not sure where that came from - I confirmed that she understood that this isn't an elite upgrade. Anyway, called back later and got taken care of, very nice agent was able to confirm on my connecting domestic flight as well.