You would need to port out, then sign up for a new account with a new email address and port back in. If you decide to port out and back in and go through the potential aggravation, you would lose any referral credits you may have accrued on your existing account.
Unfortunately, the promo pricing is for new customers only and a marketing gimmick to bump subscriber counts (while alienating existing subscribers) IMHO but serves the intended purpose.
