I am not sure if the server of emule supports this feature. But I believe this is doable(don't quote me, I am not an expert). The "show details" for "friends" doesn't usually work because most of the time, emule doesn't automatically try to locate your "friends", even if they are online. But if you are somehow able to know the server he is on, you can connect to him through "server connection" by being on that server yourself.
I have tried "adding sources" by enabling "advanced control" and entering user ip and port, this sometimes work but most of the time it doesn't. Connection through server is the best.
Another idea is to locate a user using the user hash. I wonder if this is possible. But if every user has a unique hash, why is this not possible? Why do we have to know the user ip and port? Plus, I know of a user who changes his ip everytime he comes online( the reason i know this is the same person is because his Funnynick is always the same in MorphXT and he is also one of the few people (<3) who is the complete source of the rare file I want. He frequents the same server, has the same port (5555)but always has different ip). Using user hash to locate someone would be best.