Ezra declared that the curses in Vayikra be read before Shavuos and those in Devarim before Rosh HaShana (Megillah 31b). How was that accomplished by those in Eretz Yisrael who had a triennial system for reading the Torah?
They would take out a separate Sefer Torah and read the curses, in addition to the standard weekly parshah.
Source: I heard it directly from a well-known rav, who based it on the Rambam Hil. Tefillah, 13:1-2.