In general, I cannot say borei pri hagafen on behalf of another, if I'm not also drinking wine and making the blessing for myself as well. (Shulchan Aruch Orach Chaim 213:2)
One exception to this rule is the shabbat morning kiddush (Rema to Shulchan Aruch Orach Chaim 273:4). There I can say borei pri hagafen to allow someone to fulfill his obligation of kiddush, even if I am not drinking anything.
What happens if there are two other people present on shabbat morning who both wish to drink wine, but one has already fulfilled kiddush?
I don't want to drink wine, but I can say borei pri hagafen on behalf of the person who has not yet fulfilled kiddush. Can the second person, who has already fulfilled kiddush, use my blessing for the wine he wishes to drink now?