Apply the same approach for Omen.
Find a visual indication. Since he gets through the opponent use that as a starting point. From there finde the manual cancel window. When youre near it start double tapping.
Then when the timing hitting the manual is down apply a special cancel technique like yours.
But i hit the lab extra for the OP to get the manual timing for his heavy manual of heavy slide down.
Since i use the approach myself and never played Omen i let him know what he should watch for.
I just tested it. You should watch for the standup animation of omen at that point doubletap the button.
But you should know that due to the fact that only the far normals can be used it is harder to do. They all have 10f startup except for sweep 8f (which is 100% succes rate for me at least). For the other normals just grind it out.