Thank-you emails (which provide a link to the buyer's thank-you/download page) can only be sent to the buyer's email address; this ensures delivery of the link to a valid email address known to be associated with the buyer.
We have no way for PayPal buyers to specify the message/link should be sent to any other email; however, if you accept credit cards (as an alternative to PayPal), the buyer can enter any email address they wish on our secure checkout page.
Typically a gift buyer would simply forward a copy of their thank-you email to their intended gift recipient, or they can even just copy the link and paste it into a personal message to the recipient. You may wish to add some text explaining this in the Product Thank-you Page HTML field (which gets displayed on the download page) and/or in the Product Thank-you Email Message field (which gets added to the standard greeting and link we'd send for that product).