AS-2 is supposed to leave residual sweetness
Zymurgy had an article comparing various ale yeasts. The cider made with Wyeast 1968 London ESB/ WLP002 was sweet.
Denny Conn recommends 1450. He said it naturally left the cider sweet.
You might try Windsor. It is a low attenuator in beer so may do well to leave sweetness in cider.
White Labs says WLP773 Scottish Cider Yeast Blend will leave residual sweetness.