Configure unicorn service script using RVM - ruby-on-rails

Question

In my /etc/init.d/unicorn startup script I have the hard-coded paths as follows:
export GEM_HOME=/usr/local/rvm/gems/ruby-2.2.0-dev
export GEM_PATH=/usr/local/rvm/gems/ruby-2.2.0-dev:/usr/local/rvm/gems/ruby-2.2.0-dev/gems:/usr/local/rvm/gems/ruby-2.2.0-dev#global/gems
DAEMON=/usr/local/rvm/gems/ruby-2.2.0-dev/bin/unicorn
UNICORN_OPTS="-D -c /home/unicorn/unicorn.conf -E production"
I am using RVM and when I change the ruby version, then the current ruby should be used for unicorn.
Question 1
So how can I make sure that these variables always point to the proper ruby?
Question 2
In my bundle I am using rack 1.5.5. Now on my production server I had to install the unicorn gem as a "stand-alone-gem" so that I can start my server using:
service unicorn start
Now the unicorn gem installed rack 1.6.x and now my Rails app crashed because rack is already loaded. Now locally I would just execute it with bundle but how can I do that when I am using this /etc/inid.d script.
The part where the server is started looks like follows, and I don't know how I could "inject" the bundler call there or if that is a good practise at all:
# ...
log_daemon_msg "Starting $DESC" $NAME || true
if start-stop-daemon --start --quiet --oknodo --pidfile $PID --exec $DAEMON -- $UNICORN_OPTS; then
The config: /home/unicorn/unicorn.conf
listen "127.0.0.1:8080"
worker_processes 2
user "rails"
working_directory "/home/myapp"
pid "/home/unicorn/pids/unicorn.pid"
stderr_path "/home/unicorn/log/unicorn.log"
stdout_path "/home/unicorn/log/unicorn.log"

Answer 1

Assuming rubyuser has all these rvm and rubies installed, one might parse the output of rvm info, running the latter from this user:
`sudo -H -u rubyuser bash -c '[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" && rvm info | grep "^ \+GEM_"| sed -e "s/^ \+/export /" -e "s/: \+/=/"'`
The command above will set the variables GEM_HOME and GEM_PATH. To just output them, remove backticks around this command.
For rvm installed in local, it’s even simpler:
[[ -s "/usr/local/rvm/scripts/rvm" ]] && source "/usr/local/rvm/scripts/rvm" && rvm info | grep "^ \+GEM_"| sed -e "s/^ \+/export /" -e "s/: \+/=/"
# export GEM_HOME="/usr/local/rvm/gems/ruby-2.1.1"
# export GEM_PATH="/usr/local/rvm/gems/ruby-2.1.1:/usr/local/rvm/gems/ruby-2.1.1#global"