You can set the persistable property to false while creating an instance of NoGeneralization.
For Example:
// Create generalization.
var generalization = domainmodels.NoGeneralization.create(model);
generalization.persistable = false;
// Use the above generalization in the domain model creation.
var entity = domainmodels.Entity.create(model);
entity.name = "NewEntity";
entity.generalization = generalization;
Good question, When I iterate over the entities in the model SDK the non-persistant entities are skipped. It not clear from the document how to do this.