Nitrous has released a package manager dubbed autoparts which will allow you to install mongodb 2.4.6.
Autoparts requires you to have a Nitrous box on version "bran" or later. If you are on version "arya" then you will need to download the contents within your box (SCP or Nitrous Mac App), terminate the box, followed by creating a new box in order to upgrade.
Take a look at the README within the Github Repo for instructions on how to use autoparts:
https://github.com/action-io/autoparts
To install/update mongodb to the latest version, run the following command:
parts install mongodb
After the installation completes, run mongo
in the console to check the version. You may need to restart the console if it is reporting an older version.