I don't know how to address the problem with those surplus females, but China should create more opportunities for or facilitate exports of those surplus males. Like trade in goods and services to complement countries comparative advantages, trade should also be used to bridge the differences in gender across countries. I know it would be difficult because those surplus males may have a high proportion of them with low qualifications, but one nevertheless should try. China has surplus in males, some others may have the opposite. So it should be mutual beneficial.
Open the border and trade! That is a way by economist to solve this issue, isn’t it?