Try this and let us know if it works for you (it works great for me). I learned about this because I don't like to ruin a whole day sampling something I may not like. First, wear a frag you know well and have apparent longevity issues with. Wait for it to dry down (I blow on the area so that this only takes a few minutes). Next, spray your ankle with a frag that is as different as possible (in terms of the notes). When you think you can no longer smell the first frag, which I assume you will spray on your arms or chest, waft the air up from the ankle you sprayed and breathe it in deeply. After doing this, you can waft the air up from wherever you sprayed the first one. Obviously, this might not be appropriate for certain social situations, but if you want to check the longevity of a frag and are not going out in public for a few hours, this is something to try.
Visit my huge swap page: http://community.basenotes.net/showthread.php?t=211135
Or visit my Sales page: http://community.basenotes.net/showthread.php?t=211407
Samples, etc. for Sale at my Crystal Flacon page: http://flacon.ambaric.net/viewtopic.php?t=282
My fragrance blog: http://bigslyfragrance.wordpress.com/