Do you mean a sleeve with the built-in wireless charging like this? http://www.amazon.com/Energizer-Inductive-Charging-Sleeve-Ic-IP4G/dp/B004QMZM8I/ref=sr_1_1?ie=UTF8

Unlike the iphone, the nexus 4 has the inductive coil built into the phone so there's no need for a sleeve. All you would need is a Qi compatible inductive charger like this: http://www.amazon.com/Energizer-Single-Position-Inductive-Charger/dp/B005QZ8BF0/ref=sr_1_2

Qi charging works through most cases as long as they're less than 5mm thick, iirc.