And are you sure what your client has in China is a sole proprietorship?  Is your client a Chinese national?  If not, I'm not sure the business could be run as a sole proprietorship.  Even a WOFE is not that simple to set up and a JV could be more likely.  If your client holds an employment visa, it would generally not permit outside employment or the operation of one's own business.

There has to be more to this story.