NDD, that's exactly right. It's near impossible.
If long-toss is "harmful", then where is the long line of players who say it has caused them injury?Funny that tons of pitchers at all levels swear by it and very, very few have ever said it caused them injury.
Why is throwing a baseball as hard as you can for distance more harmful than throwing as hard as you can from 60ft 6"? Doesn't make sense.
The key benefit of long-toss that flat ground doesn't offer is that it forces a player to speed up their arm. Chinese acrobats weren't born that way, they trained. You have to have genetics to throw 90 but I believe you can optimize your potential by learning how to speed up the arm.