Omnisphere live and Ableton Live
That does make sense. You can definitely do this by having a separate track for the new keyboard. If you run in Session View, each scene could hold a new clip with a sound or plugin for the keyboard. As the song progresses, you could have it automatically change to the next clip with follow actions or manually change. B-Wack from David Crowder Band does the same thing with the Drum Rack plugin for one-shot drum sounds.
You could also jump on the Hillsong bandwagon and use Mainstage for running keyboard sounds :) They mostly use Omnisphere with Mainstage, from all the templates they have online.