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

Just recently (today), I bought a Humble Bundle and I do not have 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? (Re-downloading and reinstalling Steam 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.