Take 2 inert train cars, weighing 100 tons each, accelerate them to 60 miles per hour and allow them to collide. At the point of collision is a discus shaped cast steel vessel which contains a graphite solid at its center. The collision simultaneously compresses and heats the graphite while forging the steel to make it harder. Much of the energy of the impact is not absorbed into the target so the two cars will bounce off each other. Hopefully not derailing the two 100 ton cars..
Supposing the crushed discus stays crushed and the graphite sample stays at a nice pressure of say 100,000 ATM, you could cook and age the sample without having to tie up an expensive press for weeks synthesizing your golf ball sized diamonds. :)
Pretty silly eh?
-Scott