No need to sugar coat it. If that's what you really think, then write it clearly: "Hey guys! Hey my fellow hackers! That poster is a... is a... CORPORATE SHILL!"
Most of my audience aren't hackers, at least not in the sense I think you mean.
And the poster is likely not a corporate shill. "Shill" has connotations of undisclosed association and intentional deception, neither of which are things I'm accusing anyone of. I don't think there's any reasonable expectation of disclosing associations on a pseudonymous forum. And I don't think most posters here are being intentionally being deceptive--they probably believe what they're saying, as most people will go through great mental calisthenics to believe what they're doing isn't harmful.
The late-stage capitalist ideologies held by much of this forum are extremely harmful, but I don't need to accuse people of malicious intent to say that. People can intend the best and do great harm.