The core won't allow you to do that. In short, the core ORs the words taken from the input string. I have explained the process in detail here: http://www.question2answer.org/qa/56561
If that hasn't scared you, then you can either modify the function I linked in the other answer or write a search module, in order to avoid modifying the core, which is the best approach. Either way, the most important thing is to keep the final SQL query as efficient as possible and try not to break the different search criteria and ordering of the core.
If modifying the query is out of your reach then you can consider this plugin: http://www.question2answer.org/qa/54072
