There are many ways to dispose of the Nichikan Gohonzon. Send it back via mail. Return it personally. Burn it while chanting the Daimoku and the Jiga-ge or, if you no longer chant, you can return it to a priest or member of another Nichiren sect for respectful disposal. Some more radical Nichiren practitioners would argue that the Nichikan Gohonzon, since it isn't a valid Lotus Sutra object of devotion, can be disposed of any way you like, including throwing it in the trash. I think personally, though it isn't a valid Gohonzon, without clearly recognizing the difference between a valid Nichiren Gohonzon and the Nichikan Gohonzon, one should, as you say, "gracefully" remove it from your life.