Thank you for sharing the requested link.
I have checked the said demo. These web demos use the Response Object Model to transfer the data to the client’s machine. The data is saved to some temporary location on client’s disk before it is presented to the user.
If your only need is to open the newly created message in Outlook, you can use the System.Diagnostics.Process.Start method for your need. All you have to do is to save your email file to some temporary location before passing it as a command argument. I believe you have already achieved this goal.