Ok, doesn't look like anyone has a solution so I bought Fotomagico 6.
You can see the difference in these two videos: this is PhotoStage: https://www.youtube.com/watch?v=cZiDdDUDJdY where the animation has a hard stop/hard start during the transition, and this is the same video with Photomagico 6: https://www.youtube.com/watch?v=5bzMUEmtz_0 with smooth animation.