If you haven't heard about the problem beforehand then asking what decision you "should" make is incoherent. You will get the result you were selected to get. There is no use talking as if you have some meta-choice.

edit: ie if you are selected on your decision process without having heard of such problems, then it is already too late to change your past decision process even if you fully understand the situation you are in. If you're capable of understanding the situation though, you presumably already had the right decision process on some level and will successfully one-box.

edit2: The probabilistic method of dealing with Newcomb's problem is to observe that one-boxers win, therefore you should one-box. This doesn't apply to the Prometheus problem; we can't observe that two-boxers probably never existed.