Do you have to attach the VPN and or Proxy to the application of WoW, or simply have it running during play?
If so, you could simply use "Hide-my-IP. Granted, it's not free; it worked proficiently and fast for me.
If he gets banned, he can say his account got hacked and the can compare the wan ips. But this won't work at all, there will be a good visiable rotation.
Playing wow 4hours from wanip 1, go to sleep and bot 8 hours with wanip2, come home from school/work play 4 hours with wanip1, go to sleep and bot with wanip2..
If you have knowledge about Linux, get cheap 6-10 dollar/month virtual private server with TUN/TAP interface enabled (ask the provider before buying) and install open***.
Pros:
You get "clean" IP.
You have complete control over server (and logs).
Less laggy than "turn the key" *** services.
Same price as the "turn the key" solution.. but you have the root access so you can install whatever you want.
Stable *** if your VPS is stable.
Cons:
Not the easiest one to install (but google is friend)
Some provider may oversell VPS nodes (too many customers on one physical machine, read the reviews).