Upload & Sell: Off
Freelensing works best with lenses with an image circle significantly larger than the sensor (e.g., something not wide-angle). Also, practice holding the lens against the mount, making sure you don't obstruct the mirror or make contact with the exposed rear element. If you are using EF lenses, another thing you can do is use the DOF preview trick to stop down the lens prior to unmounting it, which will give you some degree of control over the aperture; otherwise, a manual lens with an aperture ring can also work.
It's really not anywhere near as stupid or dangerous an idea as it sounds; it's just not a technique that lends itself to easily reproducible or consistent results. It's really about experimenting and embracing the occasional happy accident.
I would definitely NOT try freelensing with an 85/1.2L. Besides the danger of scratching such a large and exposed rear element, you can't focus if the lens is decoupled.