I spoke to my sister about her prep. She said it didn't go too bad. This is what worked for her.
She would chug a glass of the unflavored prep (several swigs to get it down). It was room temperature. Then she drank hot chicken broth (made from the little packets that the hospitals have). The salt from the soup masked most of the prep.
Of course, she did say the smell of the prep reminded her of the fish market we used to go to when we were growing up! Said if I could imagine what it would be like to taste that smell, that is what the prep smelled like!