ContravariantBindingResolver.cs

public class ContravariantBindingResolver : NinjectComponent, IBindingResolver
{
    /// <summary>
    /// Returns any bindings from the specified collection that match the specified service.
    /// </summary>
    public IEnumerable<IBinding> Resolve(Multimap<Type, IBinding> bindings, Type service)
    {
        if (service.IsGenericType)
        {
            var genericType = service.GetGenericTypeDefinition();
            var genericArguments = genericType.GetGenericArguments();
            if (genericArguments.Count() == 1
             && genericArguments.Single().GenericParameterAttributes.HasFlag(GenericParameterAttributes.Contravariant))
            {
                var argument = service.GetGenericArguments().Single();
                var matches = bindings.Where(kvp => kvp.Key.IsGenericType
                                                       && kvp.Key.GetGenericTypeDefinition().Equals(genericType)
                                                       && kvp.Key.GetGenericArguments().Single() != argument
                                                       && kvp.Key.GetGenericArguments().Single().IsAssignableFrom(argument))
                    .SelectMany(kvp => kvp.Value);
                return matches;
            }
        }

        return Enumerable.Empty<IBinding>();
    }
}