its been awhile, but as best i remember, the grease cap has a stud sticking out of it and all you need is something that threads onto it that you can either hammer or lever. I can't remember if its coarse of fine thread, but its 5/16" diameter as best i remember.
2 options come to mind. either a threaded rod, and a long nut such as threaded coupler to latch onto the cap and a nut and a big washer to pull against the outside of the hub. or a longer rod, a threaded coupler and a slide weight so as to make a slide hammer.
They're in there tight, but not that tight. the first time I had to do it, I made something and then had to do it again about 12 years ago. I made something then too.
-Michael