The content retrieval and page retrieval services now make it possible to select content (or pages) from another page on the site, regardless of the service page.
For content retrieval, for each search context, if you select the current site or one (and only one) site as the search site, you can then choose to search for content in the child pages (direct or not) of any page on the site.
The "Search context" field will allow you to select a page from the site if one of the "Daughter pages of" or "Direct daughter pages of" options is selected.
For page retrieval, if the search is for the current site, you can choose "daughter pages of" or "direct daughter pages of" and select a page for the "Search context" field.