I think that's how the original song went.
Back in the Chelsea days, Janis Joplin, Leonard's neighbor would run out every sunday morning and get back bacon on a bun for the Canadians (Leonard) of the hotel and she'd bring it back, in a sac, to eat in the sack - breakfast in bed. Leonard never ate the bacon of course, just the bun but it remained a warm memory for him that he wrote about years later - "giving me back, in an unmade sac".
His producer though didn't like it, he didn't feel it appealed to the wider American audience (they prefer greasy strips of bacon) He told Leonard he should flip that line around and so as a joke Leonard said, "what like - giving me head on an unmade bed" a total nonsense line that ended becoming quite famous.