How to use SAPI4

Question

Hello,
I have a text-to-speech application and I want to be able to support SAPI version 4 as well as SAPI5.
There are at least two methods I know of to use SAPI5:

1. Use the new System.Speech namespace, or
2. To be .NET 2.0 compatible, use COM interop (via the auto-generated SpeechLib.dll).

I am using the second method, and I can only access SAPI5 speech synthesizers it seems.
What would I need to use/do to make use of SAPI4 as well?

Thanks in advance for any help!

Daniel