At the moment is the best way to use a DOF adapter (SGBlade) with 35mm lens without spending a fortune.
It is not very comfortable, but it works!
You see in these pics that I use it with a 28-80.....try to guess how is with a 300
I made a special aluminium plate (you see it on 2nd pic) that is ready for Cartoni tripod and made esier everything.