Well I haven't changed anything in the setup, but you can get it to work, not perfectly though. If I convert the FK arm keys to the IK elbow, things work smoother, though you will get the shoulder animated during the supposed FK animation. I also had to force keyframe the torso, so it didn't have any movement during the supposed FK animation.
The first part of the animation is the converted FK, then it's switched to the IK elbow, and finally to IK arms at the end. As I said, there is movement in the shoulder during the FK and IK arms, but that's something I don't think I can get rid of.
tsm3.mov