Tie a log midline on the pull line. It will continue to pull toward the lay, until the log hits the ground.
How far away from a vehicle can it be? Multiple ropes connected with redirect blocks? How big of trees?
Can you rent a machine of any sort?
What is your local population like, out of curiousity?
P.S.
This weight in the middle of the pull line may be in Fundementals of General Treework. My copy is out on loan.
I saw a video of someone doing it a long time ago.