This isn't going to help you much but I thought I'd tell you my experience. I have the same thing happening to my brandywine tomato plant - the flower falls off just about a 1/4 inch in from the flower. I've been asking for help. Some people thought it was the high heat and humidity and then somebody suggested using an electric toothbrush on the head of the flower just where it joins the stem, the premise being that the pollen needed to be shaken a bit. I really thought that would work - and the flowers did stay on a week or so longer, but then they started falling off again. I'm still trying to find out what I can do. I'll let you know when I do.