Must save to card in "offers" tab when you log into your account.
Appears to be for only American Express issued cards (not bank issued) at this time.
MYER GIFT CARD
SHOPPING / Spend $500 or more, get $50 credit
Spend $500 or more on your saved Card by purchasing one or more Myer Gift Cards online before 31 May 2014 to receive a $50 statement credit. Limited to the first 10,000 Cards to save the Offer.
Please read the Offer Terms Show the Terms for this Myer Gift Card offer
EXPIRES
31/05/2014
Offer only applies to spend on this Card. It does not apply to spend on any supplementary Cards on this account or any other American Express Cards you might hold.
Card Members must spend $500 or more on their saved Card by purchasing one or more gift cards online at Myer Gift Card, between 29/04/14 and 31/05/14 to receive a $50 statement credit.
Offer applies to Myer Retail Gift Cards only. Offer excludes Myer Corporate Gift Cards.
Participation is limited to the first 10,000 Cards to have the Offer saved. Limited to one statement credit per registered card.
Statement credit is normally issued within 3-5 days of the eligible spend, but may take up to 10 weeks to appear in your account.
Statement credit may not be applied to your Card Account if it has been suspended or cancelled and may be reversed if qualifying purchase is returned or cancelled.
Full terms and conditions available here
Thanks OP.
Though note:
Delivery option
When ordering multiple cards you can select to send through registered post and email.
Registered post delivery:
Posted Gift Cards will be presented in a personalised greeting card sent via Registered Post ($4.95 delivery fee applies).
Email (Digital Gift Card):
Digital Gift Cards will be delivered directly to the nominated email within 4 hours.
Digital Gift Cards must be printed to redeem in store or download into Apple Passbook and can ONLY be redeemed in store.