The sponsor doesn't have to live with beneficiary.
"I will start working in this position when I get my EAD."
^ this, in my understanding, is the key reason why you can't use your future income. Firstly you'll have a break in employment, secondly your employment is conditioned around receiving EAD.
As I mentioned earlier, if you had work independent of your AOS and income from it - then I'd say there would be a possibility of using this income. But even then USCIS can ask for joint sponsor.
What you're trying to do is not much different from somebody having no job saying they won't need a sponsor because they'll get a job once they get EAD / GC