Here is a great tip on adding filters to your PivotTable even though the Filter command is greyed out in the Ribbon. I had the pleasure of meeting Mr. Exel Bill Jelen at a seminar he put on in Pittsburgh last week and this is one of the tips that was in his presentation. I hope you find it useful.
You can download the file here and follow along. If you get a preview, look for the download arrow in the upper right hand corner.