Anule el valor inicial de incremento automático de la columna Id con Fluent nHibernate AutoMapping

I'm using Fluent nHibernate AutoMapping for a project and would like to change the initial Id value for one table in my schema from 1 to say 1000 (all other tables I would like to remain with the default behaviour of starting the Id at 1).

I'm guessing that I need to specify this in my IIDConvetion, but am not sure how?

public class PrimaryKeyConvention : IIdConvention
{
    public void Apply(IIdentityInstance instance)
    {
        instance.Column(instance.EntityType.Name + "Id");
        instance.GeneratedBy.Native();
    }
}

Would really appreciate being pointed in the right direction.