Ok, take 3, and I apologize to everyone else for the spam, but I think this will be helpful to have in the archive.
So it turns out my overly optimistic and naive assumption that client\jvm.dll would be sufficient was way off. Looks like it needs the full structure, including dlls/jars in ..\bin and ..\lib.
While I could copy all of these, I still know that a given JVM is installed on each client, so I'll just point to that. The only thing left is to determine whether it's in "Program Files" for 32-bit, or "Program Files (x86)" for 64-bit.
I also finally found my old prog_guide.pdf and customizing_guide, but to save me some searching, do you know if there is there some simple dir_exists() or file_exists() type thing so I can conditionally set my javavmpath accordingly? Are those PDFs the best place for ACL reference?