A temporary workaround while I figure out a new gift certificate solution! It's a bit clunky, unfortunately, but it's what I've got...
When you purchase this item, I will manually issue a single-use discount code within 48 hours (often sooner) which you may present to the recipient in any way you'd like.
Here's where it gets clunky: discount codes can't be applied to shipping charges (presently $3 within the US) and can only be used on a purchase equal to or greater than the value of the gift certificate; however, I am happy to refund shipping charges on orders over $25 (my current free shipping threshold) or issue multiple smaller discount codes if you want to give someone $100 or more of store credit.
(The holder of the discount code may at any time also email me to ask to redeem their gift certificate manually, thus avoiding paying for shipping, but I am only one person and I have to sleep sometimes, so I can't promise that I will be able to respond before the item sells - hence issuing a discount code that can be used without any involvement from me.)
Like I said, it's a workaround...