Exactly what I did, but I was a 64 lock and I didn't enslave the felguard, I've enslaved another demon from there which was 68 elite (felguard was 67 elite). Took me some tries to get to the elephant without the demon breaking its chains, but finally I did it. My demon died at about 20% and because the elephant's speed decreases after this, I could kite him and kill him.

Thanks Blizzard!