I want to add env variables to new instances

I want all my deployments to have access to postgres, thus I'm creating a plugin which sets up a new user with access to a new database (on a postgres server in a different container). I want to expose the database access with an env variable, just like heroku does. To me it looks like release is the best place to put this hook.
Build image from Dockerfile instead of curl S3
Redeploy apps on reboot, fixes #82
Merge pull request #178 from asm89/redeploy

Redeploy apps on reboot, fixes #82
Merge pull request #134 from phaza/patch-1

I want to add env variables to new instances
Merge pull request #168 from Kloadut/docker-build

Build image from Dockerfile instead of curling S3
remove leading 'remote:' from git output
Merge pull request #179 from kubenstein/master

Remove leading 'remote:' from git output
Remove redundant command from dokku-standard plugin
Fix that only the output the last plugin command is shown

Plugin "commands" should end with "cat" because the output of each
plugin's command is piped through the next one by pluginhook