Forcing Nexus 5 to charge wirelessly even when USB device connected
As far as I can tell  and from links like this and also  this link (for different devices obviously) it seems that once the USB is plugged in that is what will charge the device, and the wireless-charging is disabled. 


  The Nexus 4 has two main power circuits: 1) Battery Connector &amp; Charging Circuit &amp; 2) Wireless Charging GEN2 Circuit. These two work together with internal battery protection circuit as well. There are many controls going on while charging, such as current sensors, thermal sensors, voltage reference and voltage input detection. So basically it has been thought to avoid any problem if you happen to connect both charging supplies at the same time, as only one will act as the charger, and as far as I can understand the logic of it, it’s the USB charging that has priority over wireless charging.