Why search the preview site at all?
Not sure if I fully understand the question. You want to allow users to search for .page files using LSCS?You could change deployment descriptors to publish *.page files to LSCS. Assuming they were tagged in a meaningful way you could then search for them using normal LSCS queries.
I want to enable a site level search to the end users that they can search for keywords that are on the .page files.