Some of the guys here have more experience with ES. I thought that u have to press out the original metal sleeve, but apparently not. This is what ES has in their FAQ:

6) During control arm installation, how do I remove the rubber part, when reusing the outer metal shells?
Answer: The easiest way to do this is with a propane or butane torch. Leave the shell in the arm and heat-up the outside of the shell. Once the rubber bond starts to break, the rubber will boil. Be careful not to melt the shell by using even and sparing heat. Once the bond is broken, push the rubber out with a screw driver or other tool.