Well, I've got a bit of a dirty hack working.
I downloaded this tool, also has source code:
Basically a tiny little java commandline program. Have to install the java SDK to get it to work. First, run the compile .bat. Then you need to make a tiny mod to the run batch file, and change the first %1 to %~1, otherwise it won't accept folders with a space in them. The batch and the .class file also need to be in the folder that contains the folder you want to cache. Then just drag and drop the folder (or file) onto the batch file, and watch it load everything. When it's done, hit enter and it drops from active memory right into the cache.
Works like a charm. Tested with path of exile, which normally takes over a minute to load off a HDD. Just dragged and dropped the folder, it took a while to preload everything. Fired it up.....16 seconds.
So the theory works, it's totally doable, I'm just hoping someone can take the foundations here and build it into a much more elegant tool.