The pin you marked with <?> is the key to USB OTG. In order for your stick/card to work, you'd have to connect that pin to ground. Then, when you wanna charge/access the phone (from a computer), you'd need to disconnect that pin.
The main problem that I see is that there isn't enough space between the original cover and the phone/battery. The second problem is that our beloved Nexus is old and many thinkers moved away to newer devices. And, to access the USB port internally, you'd have to open the phone, which would void the warranty (if the phone still has one).
PS: Still remembering those kind of math exercises from high-school :P