I think you need a wheel puller. Sometimes shaped like a Japanese bell or like a Chinese hat; goes over the hub (or screws into the hub) and has a bolt in the center that screws down on the axle. Do not use the spokes as a point to get some purchase. They will break. If you were running, you could back off the castle-nut a couple threads and drive around a while. You can also try heat. These wheels can really be stuck on, so be patient.
Here's one on ebay [cgi.ebay.com