Using SAPI is there a way to enter pinyin for Chinese pronunciation?

The goal is to be able to pronounce something like wo3. System.Speech can handle Chinese characters, but is there a way to input pinyin directly? It seems from http://msdn.microsoft.com/en-us/library/ms720566(v=vs.85).aspx that I should be able to write out the pinyin like so

<PRON SYM="ni 3"/>

How do I use PRON SYM?

Update: Here are some web pages that discuss the issue but with no solution: - http://www.ms-news.net/f3012/problem-with-phonemes-and-chinese-tts-3031240.html

Update2 I am using System.Speech.Synthesizer in .NET. Perhaps this is the issue. I can see that entering it into the Speech Properties works fine:

If I do this from C#, it just reads the tag:

        var culture = CultureInfo.GetCultureInfo("zh-CN");
        var synth = new SpeechSynthesizer();
        var voices = synth.GetInstalledVoices(culture);

        if (voices.Count > 0)
        {
            synth.SelectVoice(voices[0].VoiceInfo.Name);
            synth.Speak("<pron sym=\"ni 3 hao 3 xiao 1\"/>");
        }