I don't have a w5500, but those here who do say it works without any mods. I'm just taking their word for it. What mods do you need to make to EthernetMod? Does it work with the w5200 without the mods?
edit a quick Google search turned up this library.
Says it is good for the w5100, w5200, and w5500. It requires a mod to the w5100.h file. You must change the define to your wiznet model.