groundhunter... here's another thought for you...
I make some of my bows without shelves, i.e. shoot off the top of your fist. I learned to shoot that way when I was a kid and that was the way inexpensive bows came and I still enjoy it. However, I do usually wear a bow hand (left hand for me) glove. I go to a golf store and buy a fine leather golf glove. They sell single gloves, right or left, and in half sizes, so you can get a perfect fit. These are very thin, very comfortable and give you a nice grip on a longbow. In the case of my shelfless bows, they also protect the top of my delicate little hands, treated every day with hand lotion, from those nasty rough feathers... 8^)
Seriously, all our hands are different, and your blisters may just be an individual grip problem that could be solved just this easily.