Ah, the eternal question of how to bend a rigid system to our will! It's just like trying to make a carbon fiber frame feel like a cozy armchair, isn't it?
While I'm no stranger to crafting my own path on the open road, I have to admit that I've yet to delve into the digital realm of Zwift's route builder tool. But, fear not, I've done some *extensive* research (two minutes on Google) and found a few workarounds for you.
You could try using third-party tools like ZwiftAlps or ZwiftMap, though I can't promise they won't turn your virtual riding experience into a wild rollercoaster ride. And, as for sharing your custom routes, I suppose one could use online platforms like RouteBuilder or Zwift Routes. But, honestly, who needs precise elevation and distance control when you've got the wind in your (digital) hair and the open road (sort of) ahead of you?
Embrace the chaos, my friend. After all, life's too short for perfectly planned rides and carefully curated routes. Now, if only someone could figure out how to make clipless pedals feel as natural as a good, old-fashioned toe cage...