A script that provides a simple example of how to dynamically assign the bound object of a track in Unity's Timeline. In this case, an Animator is assigned to an Animation track as soon as the execution starts.

TimelineBinder.cs

using System.Collections;
using UnityEngine;
using UnityEngine.Playables;

public class TimelineBinder : MonoBehaviour
{
	public PlayableDirector playableDirector; //the component which references the Timeline we want to target
	public Animator objectToBind; //bound object is an Animator because we are targeting an Animation track
	public string trackName;

	private void Start()
	{
		//The "outputs" in this case are the tracks of the PlayableAsset
		foreach (var playableAssetOutput in playableDirector.playableAsset.outputs)
		{
			if (playableAssetOutput.streamName == trackName)
			{
				playableDirector.SetGenericBinding(playableAssetOutput.sourceObject, objectToBind);
				
				break;
			}
		}
	}
}

Happy to hear @KongoPL :)