Charge iOS device through mains whilst using data cable with laptop
Rather than having to deal with a homebrew solution, why not just purchase an externally powered USB hub? For example, the D-Link DUB-H7 USB hub is able to provide 1.2 Amps through 2 of its 7 total ports (labeled as 'fast charging' ports). There may also be other hubs out there that will offer the maximum 2 Amps per port.