It shouldn't be too hard to come up with a kernel extension that allows you to do this - in fact I wouldn't be surprised if there already was an undocumented io

It shouldn't be too hard to come up with a kernel extension that allows you to do this - in fact I wouldn't be surprised if there already was an undocumented ioctl() that links a particular inode on a file system. Alternatively, the sledgehammer method is hitting the power button: a fsck should be able to pick up the nonzero refcount and make it available in lost+found. (depending on the file system)