What is the recommended way to autostart a Postgres cluster using a nonstandard data directory?
Are You using the official packages[1], supported by the PGDG?

You can do 2 things:


edit the startup script file (or make a simbolic link) pointing to the new directory.
Edit the /etc/postgresql/[version]/[cluster]/pg_ctl.conf to point to the new directory;


Please, take a look a documentation from debian website[2] to see more details.

EDIT: Looks like what you are looking for it's the pg_createcluster[3] utility.

Hope it helps!

References:


http://apt.postgresql.org
https://wiki.debian.org/PostgreSql
http://manpages.ubuntu.com/manpages/trusty/en/man8/pg_createcluster.8.html