There is a tool out there called "Magical Jellybean Keyfinder" or something similar; I believe it supports a command-line option to output to a CSV file. You could write a script that runs that, then parses the CSV file and then either builds an NSI and puts it in the \Inventory folder, OR writes it to the registry where you can pick it up via Custom Inventory.
One caveat; some antivirus programs detect it as a "hack tool" so you may need to exclude it from AV scanning.
A note on the command line syntax:
keyfinder.exe /savecsv c:\temp\ /close /file myregkey.csv
The trailing \ on the path is required from what I found in my testing.