I don't want to try to fool the audience. It likely won't work and will come off as a cheap trick.
I do, however, want to plant doubt in the audience's minds. I want them to at least consider the possibility that Melkor's repentance is genuine and that he's on a different path now. I want them to question their conclusion that 'obviously' Melkor is bluffing.
So, when he turns out to have been bad all along, they will feel somewhat vindicated - told you that wouldn't last - but in the moment of these 3 or so episodes, they have to wonder if the other characters are right about him or not.
That means that Melkor can never give the game away, speak directly to the camera, or reveal his plans to a confidante. It doesn't necessarily mean he can't behave suspiciously. There just has to be at least one plausible explanation of what he is up to being above-board.
I like ... but I'm afraid after hearing Professor Olsen on the live session say he doesn't even want a HINT to the audience, it'll get shot down :-( BUT, we can hope!