This is an old thread but I thought this may help. I was given a wheel with a Campagnolo rear hub and a 9-speed cassette that was very hard to remove. Using a chain whip and hammering on an adjustable wrench on the correct tool wasn’t working. After reading through this thread, I had an idea, and it worked wonderfully.
After soaking the lock ring overnight in PB Blaster, it still wasn't budging. So, I put the tool in the lock ring and held it in place with a skewer, then chucked it up in my bench vise. I put my chain whip on one of the larger cogs and used the hammer to tap it in a counter-clockwise direction. Voila! It started turning, though reluctantly. I hope this tip may help someone in the same situation.