Thats a great cost saving measure that certainly needs to be given a go.
Therefore I suggest since the pilot salaries far outweigh those of cabin crew and savings can clearly be made in this area by room sharing you can trial this clever idea first for say 12 months and if it proves to be the cost saving initiative you say it is im sure cabin crew would be more than willing to give it a go (I can see a few legal disputes but hey its all about cost saving).