No, sorry this does not work, either in the grid or with the custom display. No exception is thrown, but neither does anything show up — I just get an empty string.
Additionally, if I've defined the field using one of the <custom> fields and do not check the check box to make it show up in the grid (which I don't want to do because I only want to see the custom display), the definition with the new name and calculated value disappear after a save. So not only do I not get a value back, when I go back into ezEdit the field has reverted to <custom> with no calculated value.