The problem with the Nexus 4 would be that it does not have an internal SD card. It uses a Toshiba Chipset for storage.
It is theoretically possible. But you'd have to loosen the chip, and if not done by a professional the whole device will probably be damaged.
Also, if you were to plan to put a new chip in(there are bigger variants of the same chip up to 64 GB), that would be an even harder task.
Soldering it back on and getting all the firmware etc onto the chip.
I think noone did it before however. So you'd pretty much be on your own.