Keyframing would be great, but until that happy day I think the only way to animate transformations is to change the transformation property while recording. That is, enable recording on the scale, start recording, then change the scale.
You can create a take that represents a constant value, then use take blending to transition between the take's value and the underlying parameter value. Try this:
1. Import a puppet into a scene.
2. Select the puppet in the scene and disable recording for all of the behaviors in the project panel.
3. Reveal the Transform behavior's parameters and enable recording for the Scale parameter.
4. Set the value of Scale to zero.
5. Use the Timeline->Record 1-Frame Take menu command to create a Scale take that represents the zero scale value.
6. Set the value of Scale back to 100% (click the x next to the control to reset it).
7. Zoom in the timeline to view your take and extend its out point to make it longer.
8. Select the Transform Scale take, zoom out and drag the right blend handle (a square with a diagonal highlight) to the far left.
9. As you look at the take, it visually displays that the start of the take will use the take's value (0%) and the end will use the default value (100%).
You'll be able to apply this pattern to Position X, Position Y, Rotation, Opacity and lots of other behavior parameters as well.
Let me know if you get stuck by any of these steps and whether you have questions.