Beside fighting with abusing free satoshi system, they are also using it to prevent loss due to Multiply BTC game. I've asked similar question long time ago that A) similar case which multiple accounts being used to claim the Free BTC vs B) multiple accounts but don't claim a single peny but to be used for Multiply BTC game only... the second case was not an abusing case but violated "one acount per user" thus users can't have an easy way to beat the system (don't hope for William Hill like which you can play multiple hands).
Regarding to the "same network of IP addresses" this prove half/half chance of being honest vs dishonest. i.e: the same user doing it vs multiple users doing it. For the case of multiple users doing it there is a scenario that you refering people to the site with your guide, tricks, etc... and your methods involving using VPN service which you will be also benefit from the VPN provider referral system, thus your users using the same service and expecting they will all assigned to the same network/subnet of given VPN traffic outgoing point. For the case like this I think you can't fight back with hope in case their fingerprint technology involve only one criteria which is the LAN IP & Public IP.