Adding something to jna.library.path on OSX

I need to added a bin directory to jna.library.path to get Rococoa w开发者_StackOverfloworking on OSX but I can't seem to figure out how to do so. Inside java when I call System.getProperty("jna.library.path"); it returns null so this won't give me a clue about where to place the bin directory. Any ideas?

java -Djna.library.path=path\to\bin