1) Download reader from link in this post (single and multipart archive are the same)
2) Just run reader as every other game. Just. Run it.
Figured that out in the interim - it's been a long time since I first learned about Ren'Py so I forgot that each game has its own executable file to run it, rather than running it through the Ren'Py executable itself.
Personal favorites, by game:
Millennium War Aigis (RIP): Liana
Girls Kingdom (RIP): Iris
Dragon Tactics: Memories (RIP): Diske
Brave Girl Ravens xR (RIP): Francette
...Most of the games I play on Nutaku end up getting taken down. Hmm.