Sorry for wasting your time, I think I was wrong to raise this bug and it can be closed.
I see that /usr/lib/x86_64-linux-gnu/OGRE/cmake/OGREConfig.cmake defines OGRE_PLUGIN_DIR, and that this path contains a plugins.cfg file that includes the correct PluginFolder filepath. Therefore, no magic is required - I simply needed to pass this variable to my application. Thanks again for maintaining this package - and thanks also Andreas for moving on my report to the correct list, Matthew
