I tried setting up a two-step button that looked like this:

Step one: E to all Windows
Do not advance to the next step for 1.0 seconds
Step two: nothing
Do not advance to the next step for 1.5 seconds

I played with the timing for over an hour. For whatever reason, when you're casting a channeled spell and you hit another ability EVEN WHILE YOU'RE ON THE GCD it will cancel it. I tried different timings paired with different ability-que settings in game. Meaning, no que, short que, full que. Still, no dice.

Without [nochanneling] I'm just not that impressed with channeled abilities.