The only thing i can think of is to add fabric to the back or the front by going through the arms-eye. But guessing that you bought the shirt from a department store to lengthen or match fabric is going to be hard. Going to a men’s clothing shop wont help either since the cut of most men’s shirts are built as a bag shape first then they tailor them to fit sizes. Your best bet (I know you don’t want to hear this but coming from a women with a big bust) is to keep shopping around for that perfect fit.