I opened up the following issue recently: http://aspnetwebstack.codeplex.com/workitem/463
I am not sure if it will be implemented so I decided to dig deeper and implement it by myself but that attempt was a failure :s Validator provider extensibility point seems complicated to me. However, I am sure there are good reasons why that part has been structured that way.
What is the most elegant way to implement this feature by providing a new validator provider? Would it be better to override the some parts of DataAnnotationsmodelValidatorProvider? Or should we follow a way where we will create a brand new provider?