i think it won`t work either way.
think about it like this: a web page you`re loading is trying to access a file on the hard drive. if it was possible, i would be able to write a jscript, on a webpage, that could read some file on your drive. read and then post it to my server, perhaps? no way you`d allow that! so, i`m no expert in this area, really, but i think that the only way to do it is to either modify your browser somehow (userscripts, mods, whatever) or have them loaded from a different directory, one that would be registered in your browser as safe.
that`s what i`m doing in my version of client - i`m both modding the browser (firefox in this case) and loading files from a safe directory - the extension`s directory...
in Opera you can use userscripts in js, so probably i should not be too hard to port my mods so that they can be used there... someone did try, afair, but since then i`ve added several functionalities that depend on the way mozilla does things, so it might be pretty painful to port it
but i digress.
try writing a website, any website, that`d try to access diferent files on your hdd, in opera`s folders. if one of them works, you can write yourself a simple script (mine may work, actually) to rewrite the links Stephen`s client provides, and do it each time you load a GC page. that`s what i do
if i`m wrong in any of this, please disabuse me....