As the U.S. has essentially 5 power grids, they would need a more detailed database too. Still, fascinating stuff.
But that might not be enough - the original signal is still there, and it's much stronger than your noise. The frequency is still powering your power supply, and still causing a 60 hz variation in the voltage.
You would need to isolate the power supply completely, or run it entirely through your noise adder. It would work best if you could add the noise to the DC output of the power supply.
This would provide the signal noise filtering and phase-locked-loop (e.g. the necessary +- ppm signal power spectral distribution control).
Given propagation losses, my ENF signal doesn't have to be nearly as powerful--merely more closely coupled to the device(s) being "shielded".
Also, I think a so-called fast-switching DC-to-DC converter would provide the necessary isolation. Plenty are being manufactured now that isolate down to 40Hz, but outside of the audiophile realm, that quality of filtering isn't typically used for low-power applications.
I think we have our new line of CSI dialogue right here.
Followed closely by "I think this case just had -- [puts on sunglasses] a shocking new development."