To install a package to a specific directory with pip use the following:

pip install <package> -t <directory>

Addendum: After to speaking to one of my friends who read this he posited the question 'When would you ever need to use this?'. Well an example is if you don't have access to the default pip location (e.g. webfaction servers) you can make a directory where you do have access and store all the installs there.