You would need a driver, a TCP/IP stack, changes to the software so you can search for aps, turn the wifi on/off and connect to access points and input wep/wpa keys, and some other software changes for loading/transferring the files. All this is not trivial.
Honestly, if you wanted wifi you should have bought a different reader - I don't think all this will happen anytime soon. There are readers with wifi out there, in fact, I don't particularly desire wifi on my reader, although I would kill for better large library handling for my Sony.
You best would be contributing to/supporting
OpenInkpot, there is some effort going on the Sony front, although nothing you can install as of yet.