Jython AMF gateway: coercing a java bufferedreader into a StringIO?
It looks like PyAMF support on Jython is working reasonably well as of now: 19 unit test failures, most apparently bytestring permutations, assuming a forthcoming patch to PyAMF trunk to remove test_sol use of os.tempnam and going against the asm branch (basis of the 2.5 alphas); that's a fair amount of qualifications, but that's development!
StringIO expects to be fed with strings, either at construction or via write(). So it should be reasonably possible to do just that. Note that doesn't exactly play well with what BufferedReader is trying to do.
You might be making it too difficult for yourself. I'd recommend looking at modjy (http://www.xhaus.com/modjy/), which will shortly be a standard servlet wrapper for Jython. It supports the wsgi protocol, so any code you write would actually be portable between Python/Jython, not just with servlets.