A good trick (although, somewhat dangerous) to removing the spring retainers, is to take a socket that's just big enough to fit over the head of the nut but still over the retainers, and smack it with a hammer.
Seriously....wear eye protection and it's probably a good idea to wear a glove or something, but what you're doing is basically making the spring compress a little so that the retainers can pop out. This way you won't need the compresser tool.