if (beingsimulated()) pickboxb(); else pickboth_boxes()

This strategy is discussed in the follow-up article.

In general it's difficult, because by assumption Omega has the computational power to simulate more or less anything (including an environment matching the world as you remember it; this might be like the real world, or you might have spent your whole life so far as a sim). And the usual environment for these problems is a sealed room, so that you can't look at the stars etc.