I dunno, that wouldn't work again. Most Chinese people are essentially in denial about Tiananmen--they deny it happened, deny it's severity, blame it on outsiders and troublemakers, and, especially, they accuse outsiders of exaggerating it. Remember that they're used to a biased media, they take it for granted. It's natural for them to assume that our worldview is doctored, just like theirs is. With that assumption, it's safe for them to assume that our version of Tiananmen is hyperbole, intended to undermine their government (which...I mean, honestly, it's not like they have no grounds for suspecting our media...)
This is possible because they only ever got an after-the-fact, doctored version of events. In those days, you could cover it up.
Now? How would they suppress the storm of blog posts, YouTube (or equivalent) videos, images, cell phone messages, etc, that would accompany such an event? They'd have to shut the entire country down--and even then...well, in 1989, there were (relatively speaking) a handful of cameras in Beijing. Now, counting cellphones, every person has at least one (well, anyway, there's one per-capita in Beijing, I'm sure). An equivalent suppression would require shutting down the Internet permanently. They couldn't do it.
As evidence: there was a major earthquake in China in the 70's (not sure which one, so I don't know which to reference), many deaths, etc... The Chinese government took days (weeks?) to admit that it had occurred at all. In 2008, there was footage and images of the Sichuan earthquake on the Internet as it was happening. They can't cover things up like they used to.
And if the Chinese people had watched Tiananmen unfolding in real-time...?
This is why, in my opinion, arguments for embargoes are stupid. They end up hurting the people and strengthening governments (see: North Korea, Cuba, Iraq). On the other hand, if you freely engage in business with 'bad' countries, even obeying their rules, you get cellphones, computers, and cameras in the hands of common people. They don't need your wishes and prayers, they need your tools.