Probably the same way Thanos did in the Infinity Gauntlet comic book.
Well, a little different, because Loki can't just open up a hole in space/time to fling the hammer far away in response to an attack... but imagine Loki, in a bad way, just in front of a portal and Thor tosses Mjolnir at Loki to finish him off and save the day but OOPS! That was one of Loki's illusions and now Mjolnir is resting at Thanos' feet halfway across the galaxy. XP
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