I would try again, firmly but politely don't accept September.
Well, that worked! I went to another Apple store and acted like I had never been in for this problem before. Right away, the guy gave me 2 options: wait till Sept and get the battery replaced for free, or get a 2015 refurb model. Of course I opted for the refurb and should hopefully get it in the next 3-5 days. I did specify that I wanted one with a discrete graphics card like my current model, but they tried to push back saying my model was the base model and in 2015 the base model only had integrated graphics. In the end, they said they'll try to "upgrade" it to discrete, so we'll see.