How to jump off a building with Timeline

So I've started experimenting with timeline and cinemachine for the first time and I'm looking to make some cinematic sequences with animations I'm finding on mixamo.

My challenge is that I'm using root motion to drive the movement of my character and he's jumping off a building matrix style but I'm not sure about how to properly author the actual falling animation from a variable height.

I've tried using a looping falling animation with root motion and setting the animation offset relative to the previous clip but because the falling clip's pivot is stationary at the landing position of the animation, the clip's positional and rotational offsets aren't correct and the character floats up when I transition to it.

To remedy this, I've tried using a second animation track on the same character and keyframing the fall direction and speed of my character but this had the effect of completely overriding all the root motion positioning of the character's parent transform which is what I didn't want. I wanted my keyframed animations to work additively with the other track not override it.

Without something like this, I'm having a hard time working with these specific cases.

Do I need extremely tailored animations for every tiny detail of my cinematics or is there a way I can additively adjust my animations in timeline?

I only have 6 hours of experience with it but I'm having trouble finding any documentation on exactly how I can achieve this.