I usually carry this lens, attached to a gripped body, with the lens facing backwards between my left arm and torso. The camera body then rests against my arm and torso. I've seen a pro do this, and copied the technique. It's surprisingly comfortable once you get used to it. I usually keep hold of the neck strap with my right hand just in case.
5D3, 5D2, Sony α6000, S90 | SY14 f/2.8, Ʃ20 f/1.8, 24 f/2.8, 35 f/2, Ʃ35 f/1.4A, 50 f/1.8 I, Ʃ50 f/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200 f/2.8L IS II, 1.4x II, 70-300L, 100-400L | E-mount: SY12 f/2, Ʃ19 & 30 f/2.8 EX DN, 16-70 ZA OSS, 55-210 OSS, Metabones SB | FT-QL, AE-1P | FD(n) & FL lenses