Actually, I stumbled over that question during my quest of unifying my keyboard-layouts (Mac=Work and Linux=Private) via xmodmap.
Is that even possible? No matter which way I've tried mapping the keys on OS X, something just can't be placed in the right spot on the keyboard - mostly because many uses of CTRL are placed on the equivalent of Mod-4 (the Command key).
Unless you're just trying to simulate an Apple keyboard configuration on Linux, that is.