I should attempt to install water injection on my engine (8.2 turbo). Since my engine doesn't have any sort of air cooler this would really drop the air temp after going through the turbo. Such a system is not as cheap and simple as what you found for naturally aspirated gas engine but simple enough I could probably assemble something myself. This page pretty much shows everything you need:
http://water.lovehorsepower.com/index.html
You basically need a water tank, water pump, solenoid controlled valve, pressure switch (for detecting boost from the turbo),spray nozzle(s) and of course hoses and fittings. The only expensive part is the water pump. The kit above uses a SHURflow High Pressure pump (8000-543-23
...about $80.