I can attest from personal experience that non-professionally administered CPR can work. I have done it successfully.
I monitor my pulse rate while using a treadmill.
During my four minute cool down period, with the belt traveling the equivalent of 3 mph, when my pulse dropped to about 115, I could step off the belt and my pulse would rise to about 123.
I believe that this is telling me that the motion of my legs is contributing to circulation of the blood and reducing the burden on the heart.
Thus, I believe that CPR efforts could be improved perhaps dramatically by having bystanders to the CPR effort flexing the leg muscles or massaging the leg muscles. A device to compress the larger muscles using air pressure, like a blood pressure cuff, might also be beneficial. I'd bet that such a device could circulate quite a bit of blood without any heart activity at all.