Don't add additional weight to the forklift truck
If the truck wont pick up the load, get a bigger truck or split the load into smaller parts. Adding extra counterweight is forbidden - either human or metal!
Trying to increase the capacity of the forklift truck in this way is both illegal and dangerous.
The other way to add extra counterweight is shown below! Can you imagine what this does to the rear axle? DON'T do it!