Humble Bundle Store Games into Gifts Help

When buying from the Humble Store, to get a gift link you must chose the gift purchase option. If you haven't redeemed the game, you could try contacting their support to see if they can convert it to a gift. Otherwise, the only way to redeem it on another account is to link your Humble Account with the other Steam Account.

There's no gifting option after redeeming it unlike bundles.
Make a HB Support ticket with purchase id. Write on their HB Support Ninja twitter page. You can get in the front of the queue that way. They will unlink the game and you can send it to the winner.