It would be interesting to see how large an impact economic incentives can have (in the absence of social change; or perhaps even serving as the catalyst for social change).The only way is cultivating a culture where childbirth is good. Right now there is a negative association with anything 'poverty' and having lots of kids in China looks lower class. This is very harmful to society and I hope the opposite is pushed in every way soon.
For example, I believe that income taxes in China are still assessed on an individual basis. Imagine instead that the tax rate bracket is based on the amount of family income divided by the number of people in the family, including spouses and unmarried children who are under 18 or have not yet finished their education.
This would create a considerable economic incentive for people to have children, especially for those families that are fairly well off.
If the tax rates were to become modestly more progressive in the next few years (something I would predict), it would be easy to sketch scenarios in which going from one child to two reduces a well off family's income tax burden by nearly 20%.
While not completely life changing, it would directly ease the concerns of the many couples who say that adding a second child is simply not economical... and it delivers the largest incentive to the families Beijing would most like to increase in size.