Wow, whatever happened to "hot water sets stains"?? We use heat to set all sorts of inks, paints, dyes, etc...why would it suddenly be good for removing a natural dye like blueberry???
I'd go with Oxy Clean or some other enzyme cleaner, but if you've already boiled it or run it through the dryer and it's still there, I think you may be stuck with it.
eta: My grandmother used to use hydrogen peroxide on fruit stains and it worked well (she grew blueberries and cherries). Be sure to rinse well afterwards.