I’ve been struggling with the same problem. So far the only way (without code modifications) is to symlink the directory to somewhere under wordpress directories. That of course works on unix like systems.
__FILE__ constant doesn’t work the same way across the different php versions. However in recent versions it works by returning absolute path and resolving symbolic links. WordPress path detection logick just doesn’t seem to be able to handle the scenario..
I didn’t by the time writing, but I faced the same thing recently with another one. I also did some experiments and looks like the bug is in wordpress library function plugin_basename which, according to comments, should separate the plugin name from plugin file name, but it doesn’t do that in case there are symbolic links on the path.
