This is a type of edit Lightroom is not all that good at doing, and the reason so many photographers also have Photoshop Elements 8, 9, 10, 11 - or CS 3, 4, 5, 6.
In CS 5 or 6 I would use the Magic Healing Brush tool set to Content - Aware mode.
No doubt, paying attention to details like that before the shutter is released is easier than cleaning up post process.