On two of the larger streamers I watch they have a feature where the community gives away an item by themselves. With your system I propose it be either mods lv 1+2 and maybe VIP Silver or higher?
How it works is:
Member X says I have Call of Duty key to give away.
He types in !giveawaygame (or something) | Call of Duty 4 | KEY # HERE | TIME for giveaway| Message
So what happens then is there is an alert that pops up on the stream with the item given away by whom and time till drawing.
People type in !enter
It then picks the winner and sends them a twitch note with the key code in it.
Why?
Well larger communities have many members that have access to either games/codes or are just wealthy. This system takes the onus off of the streamer to provide the key to the winner and if it doesnt work then its on the donator and not the streamer. It also builds a stronger community because regular people can get in on the fun of giving stuff away. It also frees the streamer up from dealing with giving gifts away. Personally I get 2-3 game keys a day from viewers and while I love it, in the past the keys have not always worked. With this system I would just direct the winner to contact the donator directly. It is also a nice coin sink to keep the coffers drained and increases the value of the coin.