Can we create giveaways that's not a key?

So the only possible choice for me to giveaway the game is to buy it from Steam store and then gift it by sending them to a friend on my friend list.
But when I try to create a giveaway here, the section with keys is required to be filled. I have no other choice to fill it with the text like STEAM-GIFT-WILL-BE-SENT-THROUGH-STEAM or something like that. And a lot of users understand that, but I met some that have Private profiles and refuse to add you, one person even blocked me.
Can you guys believe this, I just tried to add them and they just block you...