This is a major exploit going around. It will allow you to have any champion skin out there. Basically you just need to select your champion while picking a champion that you have purchased a skin for. IN the video they use ashe and jarvan. He picks ashe but has jarvan selected for skins. This will allow him to have the ashe skin instead of the default one even though he hasnt purchased it. Pretty awesome exploit in the game and its working as of the latest patch. Here is a video of it in action.
[youtube]
http://www.youtube.com/watch?v=IqzbUHBopvc[/youtube]