I came up with a partial, albeit cumbersome, solution.
 
I disabled the drive in Device Manager.  Then when I launched Sonar and opened the project file, it said the audio files on the spinning drive were missing and where would I like to look for them.  I navigated to the audio folder in the project folder on the SSD and Sonar is now using those files.  So maybe it is something in the Sonar project file that is looking for the files on the spinning drive instead of the SSD. 
 
I'll have to enable the spinning drive again and see if Sonar goes back to the spinning drive or if it will continue to use the SSD. 

I think that might have made Sonar change the project file to now look for the audio files in the audio folder on the SSD.  I enabled the spinning drive and re-launched Sonar, opened the project and it went to the SSD instead of the spinning drive.  I'll have to try a new project, starting it on the SSD, to see it Sonar will look for the audio files on the SSD for projects that were initially saved that way.  Hopefully this will only be an issue on older projects I started on the spinning drive.
 
Can anyone tell me how to edit the project file so it looks for the audio files on the SSD?  I checked the Cakewalk.ini and aud.ini files and didn't see any settings for individual project files.