C# - Add A Validation Support To DropDownList By Creating A Custom Control?

I'm trying to add a validation support to DropDownList by creating a custom control inheriting from DropDownList:

public class MyDropDown: DropDownList, INamingContainer
{
private const string ValidatorID = "Validator";
private RequiredFieldValidator _validator;

[Code]....

My class implements INamingContainer because I wanted to avoid naming conflicts. Unfortunately when I try using this control I get the following exception:

Unable to find control id 'MDD' referenced by the 'ControlToValidate' property of 'MDD_Validator'

This is happening beause for INamingContainer FindControl(NamingContainerId) returns null.

When I remove INamingContainer implementation and set validator ID in the following way:

_validator.ID = String.Format("{0}_{1}", ID, ValidatorID);

Everything is working fine, and id given to Validator is the same as it would be inside Naming container.

But is there a way to accomplish this WITH INamingContainer ?