So there is another aspect to think about (this is coming from 3 years in a row applicant who had below 500 scores, and then increased to 511). Dont forget that a lot of schools have 2 year maximum, - you can only apply for 2 years in your lifetime. I do not know how many schools on your list are like that, but on mine there are a lot. So i actually had to take out great schools off my list for the third year because i was applying prematurely the first 2 years.
Also, in my my list (mostly east coast) none of the schools averaged scores, they took the last score, some - the best score. So definitely find it out. That being said, do you have an option of taking it in July? It takes a month for scores to come in, so if you take it in August, you wont get scores till September, which means that i probably will be almost october 1st when you send them all the secondaries. That is risky. Pushing it to July would be better.
But i do agree with general consensus that you should consider waiting for a year. That being said, we dont know all of your circumstances, so if you HAVE to do it this way, - make the best of it. What i would do is contact each school on your list and ask them two questions:
1) If you select that you have another MCAT score pending, would they wait to consider your application till your scores post?
2) how do they treat multiple MCAT attempts.
But yeah, submit primary early with one "throw away" school, and then add more schools ones your scores post.