How to return HTTP 429?

I'm implementing an API using WCF and the specification says to return HTTP 429 in certain circumstances.

Normally I'd simply write:

throw new WebFaultException(HttpStatusCode.NotFound);

However the HttpStatusCode enum does not contain a 429.

I can obviously cast to the enum

throw new WebFaultException((HttpStatusCode)429);

However I'm worried that this will not produce the correct result to the application calling my API.

What's the best way to create extend the HttpStatusCode and send valid (but unsupported) HTTP statuses?

From the C# Language Specification 5.0:

The set of values that an enum type can take on is not limited by its enum members. In particular, any value of the underlying type of an enum can be cast to the enum type and is a distinct valid value of that enum type.

So this is completely alright to do and would be your best bet:

throw new WebFaultException((System.Net.HttpStatusCode)429);