Dean could go with the full on Mystery Spot, let Gabriel die and wake up again a few times, only with all his memories intact, but Dean doesn't know if his powers extend that far, and he doesn't... want to permanently kill Gabriel. Somewhere in him, despite the intense pull of the Trickster powers, he can't make himself go that far, and he finds ways to rationalize it so that he doesn't question it or even realize, but that's closer to the truth.

He waits for Gabriel to fall asleep before he adds on the finishing touch; when he wakes up, his room will look like an almost exact replica of the Mystery Spot, only with a bed. That'll give Dean away for sure, but that's fine with him -- that's the point even. Gabriel should know what it feels like to be yanked around by someone more powerful than him.