This is something I hope all the vendors would offer: A chance to buy an upgrade software to a registered customer as a gift. This means, without letting the receiver know about the purchase.
Or, of course, a chance to have any software sent to the receivers e-mail paid by me, ready to be registered etc.
I've never seen a web-shop of software where you could give separate "download-when-suitable"adress to someone else, and do the paying with your own info. As far as I'm aware, the info you give on purchasing, is always inevitably attached somehow to the registering or something.
My children often ask what I would want for birthday or Christmas. I can't ask for money to buy plugins, but if I could give names of plugins and they could choose something that fits their budget, that would be very nice.