We went through this when we moved Stan to a big boy bed and the answer for us was putting a gate up at his door. But yes, there was crying. I honestly don't know if there's a way to do it with no crying, after all, Evan wants you there! How about moving away from the bed one step at a time until you are standing in the doorway? This didn't work for us but maybe it would for you?
What time does Aiden go to bed? I would be inclined to tell him that Evan has to learn to go to sleep by himself, there will be a lot of crying, but there will be a special prize for Aidan in the morning if he can stay in bed. Honestly, Evan will probably only cry for an hour or so, two at most, before he takes himself off to bed.