Thank you for reaching out and posting this question!
It’s great to see that you want to incentivize customers through gift cards. However, I’m afraid it’s not possible to add more value to a gift card that customers are purchasing, as the order still needs to be processed through the online checkout. That being said, it is possible to manually issue a free gift card to every customer that purchases $50 or more in gift cards.
Another great way to incentivize customers is through loyalty programs, where they can earn rewards from their purchases and potentially increase your conversions. Have you considered integrating a loyalty program on your shop?