Here's the scenario:
1) Ubuntu machine has many users.
2) Each user connects remotely via VNC to have access to the GUI
3) Each user installs a VPN client on theirs Ubuntu session and each connects to a different server
4) If each user visits the same website, each would have a different IP address even though they are all using the same machine
Is this scenario achievable?
Yes, I know each user could install the VPN on their own machine and not have to go through the Ubuntu machine. The key is that each "user" actually comes from a single "master" machine doing multiple connections to the Ubuntu box.
Depends on what VPN is being used, for example OpenVPN has a config dir in the users directly so it would allow seperate profiles and each user would not access the other config drive where the OpenVPN profiles would be imported. Hope this helps.