There is no way to search for the names of included pages on a page in edit mode. Finding out the name of an included page now requires manual intervention, which (if you're editing page inclusions) potentially needs to be done on every inclusion used on the page until you find the one you want. This is a very time-consuming process.
When editing a page in Confluence 3.5 in wiki markup mode, you could easily do this in a browser by typing Ctrl-F and then the entering (part of the) name of the inclusion page you want to find.
Incidentally, expecting a Confluence 4.0 user to simply view the storage format (i.e. XHTML) to find these page names is not an acceptable workaround - especially if you're not going to provide them with a way to edit this XHTML content (in an indented readable format).