(Spanish) Giveaway - Keys and new sets of Dota 2

Hello,

I would like to know if there exsist the possibility to make contests for keys of Dota 2's chests.
http://tecnoslave.com/foro/sorteos/desbloquea-keys-sets-dota-gratis-t159.html

I have one contest right now running through my forum and I just ask people to follow us on Twitter in order to make random winners between those who follow.

https://twitter.com/TecnoslaveDota2/status/398758634194075648

I would like to put this giveaway in the pool but I think there is no way to choose the item unless you buy them as a gift, am I wrong?

• The whole contest is in spanish as I am trying to spread the word aboout this game and I would like to bring tournaments of Dota 2 to Spain :)

Thanks in advance for your help.

Cheers!