And what's your problem, exactly? You want to buy tickets to give away before you've decided who to give them to? Sorry, you can't do that. There are other people who also want the tickets and know who they are inviting. You have to wait until you've decided who to invite and you can't "scalp" those tickets, because you are not worth more than any other paying customer.
In worst case, you've bought tickets and the person you invited can't come: You sell the ticket back to the venue for a refund.
This attitude reminds me of what happens al the time at hotel front desk: They're fully booked for a certain date and some people call and e-mail, asking the hotel to cancel other guests reservations to give them a room. Sorry, not going to happen. First come, first served.
And as I said in another comment, artists and venues can price and release their tickets in such a way that people who are willing to pay much more can get some last-minute tickets.