Here is a quick video I put together for adjusting white balance on jpegs within Lightroom 4
[video=youtube;CjUrKDggyvM]http://www.youtube.com/watch?v=CjUrKDggyvM&feature=youtu.be[/video]
[video=youtube;CjUrKDggyvM]http://www.youtube.com/watch?v=CjUrKDggyvM&feature=youtu.be[/video]