I'm pretty sure I posed this question a few months back, and never got a response, so I'm glad to see you raising the question again. I did research this both on the Internet and in the help file, but could not find a way to do what we want to do (open a user to a particular dictation source).

The following is quoted from
the Quick
Tips and isn't exactly what you are looking for but may contain enough
information for you to put it together and if you are successful, please post
back with your results so we can add it to the KnowBrainer knowledge base.   See following:

Preset to Open Any User
Automatically:

1. 
Create or locate a shortcut to NaturallySpeaking

2. 
Right click on the shortcut and select properties

3. 
Change the following text in the Target box from ~

"C:\Program Files\Nuance\NaturallySpeaking9\Program\natspeak.exe"

to the following ~

"C:\Program Files\Nuance\NaturallySpeaking9\Program\natspeak.exe" /user "Your User Name" in
Win 2000/XP

Substitute
"C:\ProgramData\users\nuance\naturallyspeaking9\Program\natspeak.exe"
/user "Your User Name"
in Windows Vista

Note: This formula doesn't work well with mult-name user
files.  Always make the name of your user
file a single word such as Bob or even Bobby_Jo_Frank.  Ditto with vocabulary names.

You might be able to get
away with a shortcut such as "C:\Program
Files\Nuance\NaturallySpeaking9\Program\natspeak.exe"
/user "Your User Name"/source
“AK5370”  as an example in Win 2000/XP but no guarantees as we've never tried this.

Lunis
Orcutt - Developer of KnowBrainer
 &

Host of the
Http://www.KnowBrainer.com Speech Recognition Forum

I have a similar requirement but have found no answer yet. I think the only way to do this would be to use what KnowBrainer has mentioned below and to put each source in as a variation on a user name.

I may be overridden on this but we'll see what others have to say.