the largest impact you can make would be to simply become a vegetarian yourself.

You can also make a big impact by donating to animal-welfare causes like Vegan Outreach. In fact, if you think the numbers in this piece are within an order of magnitude of correct, then you could prevent the 3 or 4 life-years of animal suffering that your meat-eating would cause this year by donating at most $15 to Vegan Outreach. For many people, it's probably a lot easier to offset their personal contribution to animal suffering by donating than by going vegetarian.

Of course, the idea of "offsetting your personal contribution" is a very non-utilitarian one, because if it's good to donate at all, then you should have been doing that already and should almost certainly do so at an amount higher than $15. But from the perspective of behavior hacks that motivate people in the real world, this may not be a bad strategy.

By the way, Vegan Outreach -- despite the organization's name -- is a big advocate of the "flexitarian" approach. One of their booklets is called, "Even if You Like Meat."