I haven't seen any free reg coupons but there's a voucher on the ww website to pay £12.95 for the first months monthly pass and if you sign up with that, you don't pay the reg fee.
It also says on the website that if you take the voucher to your meeting and choose to pay as you go rather than sign up for the monthly pass, you just pay the £5.99 class fee and don't pay the reg fee.