Looks like they're not honoring these digital purchases anymore so I wouldn't try this now unless you only wanted the magazine.
League Of Legends: Caitlyn Arctic Warfare Skin (And Champion) - $2
From slickdeals:
If you buy the November edition of PC Gamer you are eligible for the Caitlyn Arctic Warfare skin. If you don't own the champion, she will be unlocked as well!
Buy the magazine from CoverLeaf for $1.99
http://www.coverleaf.com/#Home&Document=59339
Send a support ticket to PC Gamer and request a code. You must send proof of purchase (you can forward the email from Coverleaf). Their email address is
PCGcustserv@cdsfulfillment.com.
This has been proven to work by many people on the League of Legends forums, and I just got my code today! (Took about 24 hours) Enjoy!
Thread on the main forums:
http://na.leagueoflegends.com/board/showthread.php?t=1232067