We have an Adobe Flex client talking to a .NET server using WebORB. Simplifying things, on the .NET side of things we have a struct that wraps a ulong like this:

public struct MyStruct
{
    private ulong _val;

    public override string ToString()
    {
        return _val.ToString("x16");
    }

    // Parse method
}

I want the Flex client to treat this as a string. So that for the following server method:

public void DoStuff(int i, MyStruct b);

It can call it as

DoStuff(1, "1234567890ABCDEF")

I've tried playing with custom WebORB serializers, but the documentation is a bit scarce. Is this possible? If so how?