You'll be hard pressed to get sorbate to preciptate as it's calcium salt.
Sorbates are typically used in <1% wt/wt concentrations for the purposes of food preservation. (1
) Which places you well within the solubility limits of calcium sorbate.
The standard means of purification (anion exchange, distillation, etc.) will destroy the cider as well. Have you read anywhere else that others have been successful in removing sorbate for the purposes of brewing?