You're referring to I-131. The problem is that this document can only be applied for while in the United States, and then one must wait and do a biometrics capture and so forth.. so, it's really only obtainable if you're going to spend a long time (potentially many months) in the U.S., which we can't do for work reasons and so forth.
(This is somewhat off the topic of my original question, but I mention this in case anybody else reading this thread is in a similar trap as we are).
