What is the difference between pretending to be on your way to Antarctica and pretending that you are on your way to Antarctica ?
Perhaps the difference is the same as with race car driving. "Pretending to be ... Antarctica" is like when children build pillow forts and play pretend. In contrast, "pretending that" requires something physical like a ticket to Antarctica or a letter from a university to join their research team. Even if the letter or ticket isn't genuine it would be different from kids pretending to be adventurers in their living room.