That is exactly what I need to do! Thank you for wording it so much more clearly than I did. :-)

I'm trying to hook into the query string & see if there is a way I can add to it or modify it so that Lucene will return the data I need to access. Each product in this system has custom fields created specifically for faceted searching. (In fact, these fields are all named "FS_something", such as FS_Color, FS_MaxWidth, etc.) The number & selection of these FS fields vary with essentially each product, which means there is no way of knowing in advance which of these fields will be available until the search is made. I am trying to build a list of these FS fields (& their available options/values) based on the current search result data set, so that the user may filter down more if they so desire.

For example, if a user searches on "paint", and none of the returned products have an "FS_MaxWidth", then I do not want FS_MaxWidth to show as a facet. I hope this explains my goal a little better. :-)