Its a bastard version.

In the 1990s I was with Mdme. Durufle at a conference. A poor soul asked about this piece and what to do with lengthening it. Mdme. Durufle looked at the person and just simply said with a strong voice, "NON."

You can do what you want, but I will always hear that answer in my head. I have sung the other verses with the chant melody. Always worked fine for me.

Mdme. Durufle was quite the lady and one heck of a player. She also protected her husband's work. I always suspected because she knew how much effort he put into composing it.

Et voila!