How to preconfigure wifi on Mac OS X (Yosemite)?

Does anyone knows a way to preconfigure a WPA2 wifi network on Mac OS X (Yosemite) ?

I'm preparing an iMac for a friend and would like to setup his home wifi while currently far away from the network.

I know all the wifi parameters (SSID, security, key) but can't manage to validate the manual setup through the AirPort wizard. I also tried to manually add the entry in Keychains but can't manage to add the confirmation exceptions on "airportd" and "AirPort" binaries in the ACL part.

Thus, I can't setup transparently and remotely the wifi connection.

Thanks for your help.