Husse, I don't think that's what OP was asking, ReFit runs before GRUB, so anything you change there will have no effect.
This page suggests you don't need ReFit to boot other OS's on a MacBook;http://refit.sourceforge.net/myths/
That method works, but you have to hold opt. every time then select OS so it's no help really.
likespie, did you ever get this figured out? I'm running Mint on my MacBook too and I no longer have any need for OSX (which always drove me banana's anyway) I'd love to hide any reference to it on boot, but would rather still have it there just in case.
If anyone else has figured this out, your assistance would be much appreciated.