Had a 4 post lift for many years, loved it.  When I bought it I whined, cried, kicked and bitched at how much the rolling jack was that fit on the rails of the hoist.  I paid the money and never regretted it after.  The jack had an air operated cylinder and the carriage ran on the rails of the lift.  Worked perfectly for many years with no issues.  Consider biting the bullet and get the correct lifting device for your 4 poster you won't regret it. 
Whipper

"There Are More Horses Asses In The World Than Horses"