True, there is a procedure for double engine flameout, and there is a procedure for ditching. But there is no procedure that emphasises the particular difficulty of ditching with both engines flamed out, that would have been useful for captain Sullenberger.
What's the "particular difficulty" of ditching with both engines flamed out that experienced pilots wouldn't be aware of?
And thirty plus years in the business and the manuals have text about consideration of water ditching.