simply transfer to Horde do the szenario w
write a ticket that your brother or so has transed your character and you dont want it...
the Gm will bring you back to Alliance
Edit: if you dont want to invole a GM wait a few days and puchase the transfer back to Alliance
edit: in EU you will get your money back for the transfer
worked for me
having the alliance AND the horde-item on my alli-char