yea. there is no substitute. when i was younger i didnt have one. so i got my hands on one of them pry-bars for breaking and moving old concrete (aparently) and wedged it into a tree.. i guess you've gotta have a tree the right shape thats strong enough. but that worked.
i've also used an I beam in a carport. with just my fingertips and a neutral grip, it works once your grip can hold out.
you just gotta find something to chin from.. its the only way..