Ah, bugger. I've lost my link to Transparent Newcomb (TN).

From what I recall, Omega doesn't let you play the game if you would one-box on normal Newcomb but two-box on TN. As a result, having the strategy 'I will one-box on normal Newcomb but two-box on TN' will probably result in you getting no money because when Omega psychoanalyzes you, he'll almost always see this. So you lose, because you're not yet past the filter.

In this problem, you were filtered out prior to birth by a Prometheus who only chose embryos that he believed would one-box. The line 'I should one-box or I won't get to exist' doesn't work because embryos can't think. At the time at which you can first consciously consider this problem, you will be past the filter, and so are free to choose the most effective solution regardless of Prometheus's preferences. So you two-box and win, 'cause you already exist.

The problem changes, of course, if there is any way in which Prometheus could punish you for two-boxing, causing you to lose >100$ in utility.

Edit: Changed a couple of details to properly refer to TN when Omega has a slight possibility of being wrong.