It's available here (for now).
http://ittc.ku.edu/~nfrisby/tcrn-plugin.tar.gz
Sorry for the whack build/test infrastructure: I wasn't planning sharing this write-once experimental code.
The 'MyTcRnDriver.initTcFromModGuts` function and the 'TcRnPlugin.append_guts` are the key functions.
The rest of 'MyTcRnDriver` is only necessary because 'tcRnModule` is a big function that bakes in its own invocation of 'initTc`. Most other functions in the tcrn don't do this. I hope to patch GHC to factor 'tcRnModule` a bit and export the pieces so that it can be re-used with 'initTcFromModGuts` instead
Note the TODOs; mostly they focus on stuff like hpc and Safe Haskell. Basic functionality seems fine.
HTH.