It's possible in r212 with the new Scene Graph feature.
Don't pin the platform to the big wall, instead use "Wall add child Platform". It will be dragged with the wall and also move with Sine behavior.
Another method: Save platform initial position relative to the wall in a pair of instance variables StartX and StartY. Run Sine for value. On every tick update platform position to (Wall.x+Platform.StartX, Wall.y+Platform.StartY+Platform.Sine.value)