I've only seen smooth back covers for extended batteries, and they tend to make the phone quite a bit thicker.
If you like my work, please hit the thanks button....!
Magnolia 1.0 for Inc 1
Magnolia 2.0 for Inc 2
Magnolia 3.0 for Rezound (coming soon...)
Magnolia Tab for Galaxy 7.7
Tweaked Stock ROM for Galaxy Tab 7.7
Magnolia X for HTC One X
6-signal Signal Bar for HTC Thunderbolt
Power Widgets for Thunderbolt
Quick Settings for Sense 2.1 Inc 2 Roms
Rosie Remaps/ordering for Thunderbolt
Probably more I can't remember...