It is (at least) the Chabad custom that the Torah Reader takes the Aliya with the curses (tochacha) in Parshat Ki Tavo and Bechukotai. The reader ascends without being called and recites the blessings before and after. (See the Luach Colel Chabad).
What happens if the Torah Reader is a Kohen or a Levi? The curses don't appear in his Aliya! And, once a Yisroel is called to the Torah, we do not call a Levi for an Aliya.
Does someone else take the Aliyah? Do we let the Levi take it, since he is not being called?