Arbitrary "files" in /proc/?

Is there a way to create files in /proc/ without actually writing a kernel module? This is for reverse engineering purposes, an app expects certain things in /proc/ and I do not want to write a kernel module to supply it. The app simply just reads /proc/something/some_key and expects certain/known values. EDIT: Union mount doesn't seem to work as I need a new directory, e.g. /proc/new_dir/ and some files in there and making union on top of /proc/ itself seems to break it.