The Halacha permits Borer (selecting) from a mixture, provided that the good is selected from the bad, by hand, immediately prior to the meal. The Poskim discuss whether Borer, under these conditions, would also be permitted to perform for someone else. The language of the Rema, in Siman 319:1 (listen to audio for exact citation), implies that it is only permissible to select for others if he is eating with them. However, the Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933), in 319:6, clarifies that the Rema does not mean to say only if he is eating. Rather, it is permitted to select for others, even if he is not eating with them. Hacham Ovadia concurs with the Mishna Berura, even though the Kaf HaHaim (R’ Yaakov Chaim Sofer, 1870–1939, Jerusalem), based on the Mordechai, is stringent and requires one to partake of the food he selects.
One does not have to partake of the food which he is selecting for others, as long as the three conditions are met.