Should have a Leiningen Clojure project in workspace.
Go up one directory
cd ..
then go to bin directory since this is already in the $PATH
cd bin
download the lein file
wget https://raw.github.com/technomancy/leiningen/stable/bin/lein
Set it to be executable.
chmod 755 lein
Tell the JVM where to find your home directory.
export LEIN_JVM_OPTS="-Duser.home=$HOME"
Go back into working directory and type
lein deps
and you are good to go.
Keep in mind that lein repl
will not work since you don't have sudo permissions.
after c9 update of 2014, c9 is working on docker virtual machine.
I've tried lein repl, and it works well.
Even you can use sudo in c9.