Select a Crowd helper. > Modify panel > Global Clip Controllers rollout > New > Choose a GlobalClip object. > Select the object in the list. > Edit > Synthesis dialog > Motion Clips panel > Track View group > New > Track View Pick dialog

Track View > Global Tracks > Block Control > GlobalClip Properties > Synthesis dialog > Motion Clips panel > Track View group > New > Track View Pick dialog

Open the hierarchy and pick a track to use in the motion clip.