Huh. I seem to have lost my original DT scripts somehow—probably when I finally uninstalled DTPO just a few weeks ago. 
Thankfully, I seem to be getting better at scripting over time! I had an older version of this script that worked on files on the file system. Adding the DEVONthink functionality to that previously took me forever, but I was able to do it in an hour this afternoon. Hurrah!
All of the instructions and associated files (I think) are written up here:
Let me know if it works and if you have any thoughts or feedback.