Buy say that doesn't work, and now you've got a skin bubble on your heel the size of the Superdome. Here's my preferred treatment regime (I'm sure there will be dissenters):
First, reduce the size of the blister by lancing it. Carry a clean scalpel blade or needle in your first aid kit for this chore, and sterilize with a match. Pop the blister from the side-just a small hole, try to avoid tearing the skin-and drain it. You then have two choices: Keep the boot off the blister, or try to minimize the friction. For the former, use a product such as Dr. Scholl's Molefoam ($3.50 for a two-strip packet) to buildup an area AROUND the blister but cutting a "doughnut" from the material and placing it so it surrounds the blister. If executed correctly, this technique will push the boot away from the blister entirely. Alternatively, apply Spenco Second Skin ($7.50 for the Blister Kit) directly on the blister. It's a water-based membrane that literally replaces the original layer of skin.
If that fails, cover the blister with some soft gauze and tape the hell out of it with adhesive tape. It'll hurt, but won't get any worse.