Games : Are there alternate methods to activate Steam CD Keys?

Just recently (today), I've bought a Humble Bundle and I do not have any access to a PC with the Steam Client...

Is there any alternate ways to activate the keys I've got from my bundle? Like calling APIs manually or external programs? (Redownloading and reinstalling Stram is NOT an option)

Or is it not possible whatsoever?

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I remembered the Humble Bundle had automatic key redemption... But it's not there anymore as the key redemption API has been shut off.