In this past (with the 1.4 nightly) setting LD_LIBRARY_PATH to the lib dir was sufficient. But apparently not any more? I'm not sure how to debug this problem, I would be grateful for any hints!
It seems that the rust-std-nightly tarball contains an identical copy of libstd-8cf6ce90.so and libstd-8cf6ce90.rlib compared to the rust-nightly tarball
If you find yourself installing nightlies from tarballs on a regular basis, you should look into multirust (if you already have, I'm curious how it does or doesn't fit your use case).
Actually, multirust is just what I need! My blocking issue was that both multirust and rust install into $HOME, blowing out my home directory quota. So instead of solving that, I tried to bypass this by just installing rust from tarballs (into a network fileshare)
If I'm reading the source correctly, you can export a MULTIRUST_HOME environment variable to override multirust's default usage of ~/.multirust. Alternatively you could probably replace .multirust with a symlink.