mkdir /var/run/stunnel/lib64 cp -p /lib64/libnss_*.so* /var/run/stunnel/lib64/ ...but if this doesn't work, you should also copy all others from all the directories mentioned in the `ldconfig -p | fgrep -e libnss_files` output.
I try it, but same problem - to make it short, I copy the whole /lib and /lib64 directories to /var/run/stunnel - same issue. So it couldn't be only caused by missing libs. :(