TAs get almost nothing from the Airlines anymore. Leisure TAs make their money from Hotel, Tour and Cruise commissions. Corporate TAs are usually paid management fees for the services they offer. The only place they may get a kickback from the airline would be around preferred carrier agreements.

That being said, most people buying a 12K vacation package would use a credit card. I don't think a travel agent would blink an eye on someone buying travel as a gift, so I doubt they care if you're going to proxy the transaction for miles.