When we are eating the meals on shabbos, my wife sometimes goes away from the table to take care of things. She asks me to serve her a little bit of food from each of the dishes as they are being passed around the table, so that she can begin eating immediately when she returns and will not have to request that all of the dishes be passed back to her. Some dishes contain mixtures of items, and she requests that one of the items in the mixture be selected for her. When selecting these items, I know that they will not be eaten immediately (miyad), as my wife is involved with something else at the time. Would this be a problem of borer?
It is not a problem because it is considered miyad. It is considered miyad for the whole duration of the meal, therefore even if she would come back an hour later, if it still during the meal it is still considered miyad
Rema O:CH 319-1, M:B 4.