There is no way to hide your IP, but you can use VPN, what makes Riot see you are playing on the same IP as your customer, or you can use Proxy if you've got bad connection with the customer. To avoid a ban from using Proxy, the customer should contact support, telling them he's the only one who plays on this account, but he is using proxy (for example because of his ISP blocking some connections, for example in China, most of people use proxies, because there is blocked access to famous websites like Google, Youtube etc.) so they should accept it clearly fine. Using VPN is easier, but not every customer is able to accept it.