I had a similar problem time ago so I added code to rebar3 for dereferencing symbolic links in *_SUITE_data/ directories.
If you are using rebar3, you can create a relative symbolic link to your etc/ folder inside example_SUITE_data/ and rebar3 would do the rest. The data will get copied to the _build/test/lib/app/example_SUITE_data/ and you will be able to access it in the test using a path similar to filename:join( proplists:get_value(data_dir, Config), "etc").
Let me know if you need more help