Because it's hard to follow that demo (much as I appreciate it), here's a more specific explanation.
×Get three wraithwings that move after the roach. In my case, once the other wraithwings were dead and I'd called out the mimic, these were #3, #4, #5, so I'll use those to illustrate. If you don't kill the wraithwings you aren't using, you might get different numbers; adjust accordingly.
Click here to view the secret text
×Get the wraithwings lined up left-to-right in the order #4, #3, #5 on the left side of the passageway, while you're five squares south of the middle one. Release the roach.
Now you can follow a pattern of SE-NW-E and the wraithwing formation will stay stable as you move to the right.
Of course, getting the wraithwings lined up in the first place is a pain... it might help to try getting them behind the door and then line them up in order to the right of the roach. I didn't try that.
