You could, as others pointed out here, invite your friends through the Tell-A-Friend system found on your account page on tibia.com and if one buy something in the webshop, be it premium time or tibia coins, you will get the outfit, and keep doing this and you will eventually also unlock the addons. The progress is also found on your tibia.com account page.
OR, you could do it the simple way, send yourself the invitation link, use it to create an account, buy x amount of tibia coins and transfer them to your main. voilà, you're now 1 step closer to the full outfit and you got the tibia coins on your main account.