Not what you wish to do, but I do it the other way around. I use my arranger keyboard as a sound module (KN7000) controlled by a Roland A-37 midi controller (to get 76 keys). The KN responds to chords from the A-37, and so I control the arrangements and I also play the Left voice from the Roland. For the KN Right voices I use the KN keyboard. However I have a Roland XV-5050 sound module which I also control through the A-37 and so I can add some new voices. The A-37 has two midi OUT's which allow this to be set up.
Regards
Keith