You can configure OpenSearch to use a search engine proxy.
OpenSearch is a collection of simple formats for sharing search string results, in order to extend existing schemas such as ATOM or RSS. The list of registered search engines is in /config/alfresco/web-scripts-config.xml. You can configure a search engine proxy so that the OpenSearch client indirectly submits a search request through the Alfresco Content Services Web Server (the proxy), rather than directly to the search engine.