GuacamoleI successfully paid for my friend's premium and admittedly it is difficult to tell that you are paying for a friend (looks identical to paying for yourself). I searched for them in the popup window that comes up when clicking pay for a friend and then clicked on their user name. This takes you to the "Select account tier" page which looks the same as the one for yourself. From here on out you just pay for it in the normal way with absolutely no indication that you're paying for a friend let alone which friend you're paying for. Nonetheless, it works.
strange, when i click their name literally nothing happens. in any case thanks for the answer, I submitted a ticket and i'm sure they will fix it (and hopefully make it more clear)