From: http://na.finalfantasyxiv.com/lodest...e/ps4/upgrade/

* Users must first register the PlayStation®3 version to their FINAL FANTASY XIV service account before upgrading.

As far as I know, this "registering" is only possible by starting the game on a PS3 while being logged in to the PSN account which was used for the purchase. But if your friend lives close to you, why not invite him/her for a coffee and get it done? But be warned: Installation is a major download orgy (8 GB from the PS3 store and 12 or 20 GB of updates when starting the game for the first time), so you might want to plan for a longer session.

After the registration is done, your friend will be able to start the upgrade procedure via the Mogry Station. After another download orgy (on his/her PS4), you should be set.