Maybe this but I am not an OSX specialist!
Unzip your file and
Right-click on the application and choose "Show Package Contents" - that will then open up a Finder window that is browsing the directory structure in there and then go to drive_c/moi/commands - that commands directory is where you can copy plug-in commands like Spurgear.

Thanks Pilou, I had dug through the package already but didn't find that subfolder for some reason until I read your message.