Hi Tom -
If I am reading this correctly, you want your servers in China to send mail for domainX.com to a server in the US for delivery.
I assume you have default send connectors in place for SMTP domains of * on the servers in China? If that's the case, this should be a simple case of adding a domain specific send connector on a server in the US, and ensuring that no servers in China
have a lower priority for the domain name in question. i.e. - add a send connector for Domainx.com with a cost of 1 to a server running the hub transport role in the US. When the transport tier in Exchange 2010 determines the delivery path for
the domain, it will follow the lowest total cost, sending the mail to the US based server for delivery.
Clearly I am making assumptions on your environment. If I am missing something in your configuration that would prevent this solution please let me know.
-Gary