I thought I saw an area where I could enable\disable languages (PHP, python, perl, etc.) for clients, but I cannot seem to find it. One of my clients is asking about getting Python setup for him.
There is no such feature except for cgi (when you create/edit the siteworx account you can toggle this on/off cgi-bin on/off)
As for the others if they are installed then they should have access to them if they have a standard non chrooted shell. If they have the chrooted shell then you can available commands to that with
jk_cp /chroot /usr/bin/command-you-want-to-install
Use this with caution.