We don't have a way to limit that list per user or role. The search index in mojoPortal and the searchable features we ship all protect the search results according to the view roles of the page and the content instance. So users cannot find content that exists on pages for which they are not in allowed view roles according to the page settings.
You can remove items from the dropdown but that would be for all users and it doesn't affect whether those features can be found in the search index, only role permissions of the content determine what can be found.
To remove features from the list you could add this to user.config:
<add key="SearchableFeatureGuidsToExclude" value=""/>
and populate it with a comma separate list of the feature guids you want to leave out. You can see the feature guid in the url when you search a specific feature.
Hope that helps,
Joe