How do I gift my extra copy of Frozen Synapse that I received as part of the Humble Bundle? [duplicate]

I recently received the Humble Frozen Synapse (And Frozenbyte) Bundles, and would like to gift my new copy of Frozen Synapse to someone. I activated all of the codes into Steam, but it doesn't seem to recognize that I own two copies of the game in the gifts list.

How can I gift this?

You can't. You only get two copies of Steam games in very specific cases.

I would have said that you shouldn't have used the key for it if you wanted to gift it, but that's not allowed either (though who knows if it's enforced).

This is all confirmed by the page where you retrieved the Steam keys:

Note: Steam will not provide you with extra giftable copies of any bundle games you already own prior to redeeming your bundle key(s).

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Note: all keys are for your personal use only.