Hi,
Currently, you would need to modify the source code (
CMS.SiteProvider.SearchHelper, CombineSeachCondition method), or write your own 
CombineSearchCondition  method or alter its result. The search mode is not related to Lucene features, it is just telling the CombineSearchCondition method how to build the searchText. 
None of these words would be just both words in the 
searchText with minus signs in front of it.   
In the \CMSModules\SmartSearch\Controls\SearchResults.ascx.cs, you can find:
                // Prepare search text
                searchText = SearchHelper.CombineSearchCondition(...
Hope this will help.
Regards,
Zdenek