Ice them after you play. After long gigs (~3 hours) on upright I would put a couple of ice cubes in a small bowl and just press my fingertips into the ice to make indentations in the cubes that fit my fingertips. I would ice them for a good solid half hour, taking brief breaks to avoid any damage. As long as you don't have fluid or blood in there, you can just play, ice, play, ice...lather, rinse, repeat forever.
Eventually, you'll get nice hard callouses that will stand up to anything. Anyting but taking a week off from playing, that is. A few other points:
1. Wear a glove on your right (or both) hand when doing dishes. Hot sudsy water is the natural enemy of callouses.
2. If you do have fluid in blisters, you need to drain them. Light a match to sterilize a pin or needle and then drain the pus. It's fun and entertaining. Then apply ice as above. I've done this procedure literally hundereds of times.
3. If you are a true glutton for pain, rip the blister open with your teeth and then play on the raw pink skin underneath. Despite the suicidal thoughts that will enter your brain, I've found that the raw skin, if stressed gently over time, builds up a nice callous.
Brian, what's up with MID players?