Are you aware of CsoundVST
http://csounds.com/manual/html/CommandCsoundVST.html
On the site it says its part of the csound source tree.
I don't know if this is possible, but to me the best solution would be to link the reaper API into a version of the Csoundvst source and figure out a way to get and set API variables from the CsoundVST code.
This would give you the ability to get the files names of items or even manipulate items, tracks, and most aspect of csound through reaper's api and have that information interact with the realtime audio state.
I haven't used Csoundvst, but if it were able to both process audio and control the API I would be all over that. Currently Reascript has no way of communicating with the audio of reaper, it is only for setting parameters of the project and items, like actions. I use JS quite a bit and I'm constantly wanting the audio and programmatic aspects of reaper to communicate.