As of the latest master, you can now cross-compile from Linux to OS-X using ENIGMA. Wiki guide here:http://enigma-dev.org/docs/Wiki/CrossCompileLinuxOSX
This should go without saying, but make sure you are aware of Apple's draconian policies before submitting a cross-compiled app to the App Store (it will likely be rejected). You can certainly distribute the app unofficially, of course (like on the "Games" page).
As always, I am happy to answer questions/fix bugs as people run into them.