In Motion 3, there's a parameter called Control Points in the Inspector that acts as the keyframeable parameter for shapes. In the Keyframe Editor, though, it's displayed as Shape Animation (kinda inconsistent).
In Motion 1/2, I don't believe there was a parameter in the Inspector that represented the overall shape. There was one in the Keyframe Editor, though. And you should be able to use the Ctrl+K keyboard shortcut to speed up the work (sets a key on the current frame for the last-adjusted parameter).