I had the same thing with GSB blades. I tried everything, a knife, a spackle blade, a file, a wood rasp, tied it to the bumper of my car with a piece of string and drove down a gravel road... Just as I was about to give up, I found an easy, sure-fire solution on-line: use a belt sander!
You'll need belts in several grits. A lot of guys start with 50, which is great if you're in a hurry, but otherwise use 80. Then progress to 120, and then finish off with 400.
There is also the problem of holding the blade. A pair of small vise-grip pliers will work, but you have to change holds to do the entire blade. Instead, get a piece of 2 X 4 (pine is okay) about 18 inches long, and nail the blade with the glue/wax spots facing up.
Regarding the type of nails, something with a wide head is preferred as the holes in the blade would allow the head of a common nail to slip through. Roofing nails will work as the head is quite large, but they are a bit soft, and may get groud away before the dots are removed. Most users report that drywall (sheet rock) nails are ideal as they have wider head than the common nail, albeit smaller than the roofing, and are made of a harder steel and last until the job is done.
If the blade becomes deformed when removing the nails, a few blows with a ball peen hammer on an anvil will quickly set it right.
P.S. Work safe! Wear safety glasses, a face shield, and heavy leather gloves.