How to achieve IValidatableObject implementation in a Potable Class Libray

Hi, I have a Portable Class Library for my business objects and I would like to add custom validation logic to this objects. I would like to do this using IValidatableObject interface and not to use the attributes approach but I havent found that possible on Portable Class Library project. Even when I have added the reference to System.ComponentModel.DataAnnotations, there isn´t exist this interface in the portable framework.

Is there solution to achieve this approach.

Thanks.