How can I hide a method with a generic return type from WCF?

Question

I have this scenario (abridged):

[ServiceContract]
public class TokenProviderService : ITokenProvider
{
    private ITokenProvider TokenProvider { get; set; }

    // BK - WCF doesn't like generic returns, so I've used an intermediary method.
    public T GetTokenValue<T>(string tokenId)
    {
        throw new NotImplementedException();
    }

    [OperationContract]
    public string GetTokenValueAsString(string tokenId)
    {
        return TokenProvider.GetTokenValueAsString(tokenId);
    }       
}

Where the only reason I implement the typed GetTokenValue because of ITokenProvider, a 'cast in stone' contract[1] interface used by both WCF and non-WCF clients. I have no wish to expose this as a service operation, and instead I use GetTokenValueAsString, and deserialize the result in a client proxy, that also implements ITokenProvider.

Yet despite having no OperationContract attribute, GetTokenValue causes the following error when I start the WCF project or try to add a service reference to this class:

Type 'T' cannot be exported as a schema type because it is an open generic type.

Is there any way I can tell WCF to ignore this method?

[1] Not a WCF contract, but a more general design contract.