Roll log.... I say roll.... Ahhh... Much better....

[5quarter]

Kbeitz...Great idea...that's roughly how I turn all my bigguns. As someone else mentioned, I use a logrite hook dug in to the top, far side of the log/cant, attached to a chain running underneath to a clevis hook which is attached to an older, heavy duty Hi-Lift jack. The I beam of the jack slides and locks into a receiver attached to the inside of the track rail. it easily turns anything I can fit on the mill and a few logs that can't.  ;)
I'm with MM on the safety thing. you need to engineer a safer way to secure the jack when turning. Nice round logs are one thing, but get a big, knarly chunk of wood on your mill and things can go south on you pretty quick.