Sorry, this is not possible without a serious amount of work. The problem is that FMOD either opens a file name, or opens a void* buffer (essentially a ByteBuffer).
To make it use an InputStream would require implementing the file api methods, and implement open, close, read, seek, tell to handle one or more input stream.
Your best option is to read the file into the ByteBuffer, but that also requires you to have loaded the file, and thus you cant stream (unless you want to get real hacky and implement an embedded http server, and stream using the fsound_net api(!)).