Asp MVC Validation - Dependent Fields?

I'm currently trying to work through MVC validation, and am coming up against some problems where a field is required depending on the value of another field. An example is below (that I haven't figured out yet) - If the PaymentMethod == "Cheque", then the ChequeName should be required, otherwise it can be let through.

[Required(ErrorMessage = "Payment Method must be selected")]
public override string PaymentMethod
{ get; set; }

[Required(ErrorMessage = "ChequeName is required")]
public override string ChequeName
{ get; set; }

I'm using the System.ComponentModel.DataAnnotations for the [Required], and have also extended a ValidationAttribute to try and get this working, but I can't pass a variable through to do the validation (extension below)

public class JEPaymentDetailRequired : ValidationAttribute
{
public string PaymentSelected { get; set; }
public string PaymentType { get; set; }
public override bool IsValid(object value)
{
if (PaymentSelected != PaymentType)
return true;
var stringDetail = (string) value;
if (stringDetail.Length == 0)
return false;
return true;
}
}

Implementation:

[JEPaymentDetailRequired(PaymentSelected = PaymentMethod, PaymentType = "Cheque", ErrorMessage = "Cheque name must be completed when payment type of cheque")]

Has anyone had experience with this sort of validation? Would it just be better to write it into the controller?