Where to install NSS modules on CoreOS?

I have written a custom NSS module and I usually install it by copying the library as follows …

cp libnss_mymodule.so.0 / lib64 /

… then I add my module to /etc/nsswitch.conf

$ grep mymodule /etc/nsswitch.conf
passwd: mymodule files usrfiles sss systemd
group: mymodule files usrfiles sss systemd

It works for me in CentOS 7, but not in CoreOS because / lib64 is on a read-only file system. Where can I place the shared object library on CoreOS that will be visible to nsdispath ()?