I've been looking for a way to add keyswitching to East West Play for Hollywood Strings, etc. I found one way to do it that seems to work - Transmidifier. It took me a while to figure out how to get it working. Here is what I did:
 

• Set up 2 ports in loopMidi
• On the midi track that will contain the 1st Violin notes, set the output to the first loopMidi port (port 1)
• In TransMidifier
  • create an input and assign it to the same loopMidi port 1.
  • set the input's activation method to Note On
  • create outputs on different midi channels in loopMidi port 2 for each articulation I had previously set up in Play
  • Set each output to use a different note (the keyswitch)
• In Sonar
  • Create a midi track for each output in Tramsmidifier. The input of each is set to the loopMidi port of the corresponding output
  • Each midi track is set to output to Play on the corresponding channel

 
Phew! It actually worked. It seems like a lot of work, but the TransMidifier setup can be saved for later retrieval. The next step would be to create an input /output set for the rest of the Play instances, each on a different input port/channel. All this to avoid having separate tracks for each articulation. 
 
Will it perform well? I don't know yet. Has anyone else tried this? 
 
Does anyone have any better ideas?