How can he use Bing as a backend? I read their API's terms of service and it forbides you from changing search results in any way.

“(c) modify, filter, obscure, or replace the text, images, or other content of Bing results, including by changing the order in which Bing results appear (but this limitation will not apply to Bing results of type "Web"), intermixing Bing results with search results from other sources, or intermixing with Bing results any other content so that the other content appears to be part of Bing results;”

I was quite interested in using Bing API myself but that does seem too restrictive. I hope you can prove me wrong!