I can't help if you want an internal clean solution.
However, if you only want it able to join a Wi-Fi network, a simple and 100% compatible solution will be connect the network cable to something like an Airport Express. And use it as the Wi-Fi receiver.
This is good for all computer that has the network port. And the bonus is that if the reception is bad, you can move the AE to a good location, rather than move the Mac, or try to figure out how to improve the signal strength.