Change Siri Search Engine iOS 9
Until today, there's no way to do this. Here's my findings:

Siri doesn't perform search directly on baidu.com, it uses Siri's hideout [guzzoni.apple.com] to relay the request over (properly configured) TLS. 

Other than asking for Apple's mercy, I think it's more probable to trade Chinese iPhone with one from another country.

BTW, the packets themselves are pretty fun to look at.