Remember, the ground terminal is a safety feature. It needs to be able to take fault current. A 12" nail in dirt will not do that. The water pipe thing may work, but only if all your pipes are metal. Most homes have plastic pipes in at least part of the house.
Many states have a code for ground stakes that are 4' to 6' into the ground near the house. You can get a nice copper stake for this at almost any hardware store. They are most often used for grounding satellite TV runs where they go into the house for lightning protection. Run at least 12 gauge from that to your outlet. I'd go that route.
Both regulators and conditioners use the chassis ground as part of their conditioning scheme. They may still help with the noise, but again, will need the GND for fault protection.
It is not necessarily the lack of GND that is your problem, BTW. It may be that you are getting appliance noise into your power line, or that the wiring into the electrical box is poor or incorrect. The missing chassis GND is more of an issue if you have ground loops from connecting multiple AC-powered boxes, like a rack effect or AC-powered pedal to your amp.