On my Brave I am able to run both a/c units, PROVIDED, I have a full 30 amps from shore power. I have resorted to using a 50 to 30 "dogbone" in many campgrounds and am able to operate both a/c units. I have a selector switch over the microwave to select "front" or "rear" with both being able to be operated when set to "front".
In response to your specific question; I believe I have read of others doing exactly as your suggest. Not sure how it is wired, but I believe it works. Do a search, or hopefully, someone will come along that has done it to explain the details.
BTW, welcome to the forum