Prime Members can get $10 credit if they load $100 onto their gift card balance. Apparently this has been around for a bit but I missed it. Posting again in case someone else has the option.
Terms & Conditions
In order to qualify, this must (1) be the first time reloading your Amazon.com Gift Card Balance; (2) you must reload at least $100 in a single transaction by July 31, 2018, 11:59 PM (PT); and (3) you must be an Amazon.com Prime Member and you must use the Amazon.com Prime account to which you are currently logged in.
• This offer is available to Prime members only.
• This limited time offer expires the earlier of 11:59 PM (PT) July 31, 2018 or while supplies last.
• The offer only applies to the first reload of your Amazon.com Gift Card Balance.
• You must reload at least $100 in a single transaction to qualify.
• For qualifying reload purchases, a one-time $10 Amazon.com Gift Card reward will be automatically applied to your Amazon.com Gift Card Balance within three (3) days.
• Offer is limited to one $10 Amazon.com Gift Card Balance reward per Amazon Prime account.
• This offer may not be combined with other offers.
• The maximum benefit you may receive from this offer is one $10 Amazon.com Gift Card Balance reward.
• The maximum single reload amount to your Amazon.com Gift Card Balance may not exceed $2,000.
• This promotion cannot be applied to any reload previously made.
• If you violate any of these terms and conditions, the offer will be invalid.
• The offer is void where prohibited.
• Amazon reserves the right to modify or cancel the offer at any time.
• The offer, rewards, and amount you reload to your Amazon.com Gift Card Balance are non-transferable, non-refundable, not redeemable for cash, and may not be resold except as required by law.
• When you reload your balance, you are purchasing an Amazon.com Gift Card in the amount you selected. This amount will be automatically added to your Amazon.com Gift Card Balance. Your Amazon.com Gift Card Balance does not expire and is subject to Amazon.com Gift Card Terms and Conditions.
• Amazon.com Gift Cards and your Amazon.com Gift Card Balance cannot be used to purchase other gift cards.
• Your Amazon.com Gift Card Balance may be used only for the purchase of eligible goods on Amazon.com or certain of its affiliated website.