Absolutely!  It's super easy.  Basically I just took a bottle cage mount like this one (http://www.amazon.com/Minoura-BH-95X-Vertical-Horizontal-Bottle/dp/B001392T2O ) and attached it on one of the bars under the bottom of my seat (right under my hips within easy grabbing distance when I'm on the bike).  Then I attached the bottle cage and made adjustments as necessary so that the cage wasn't rubbing on any other part of the bike.  In this location it's easy to grab and re-stow even while pedaling!  The mount came with some little rubber pieces to avoid metal-on-metal abrasion and it works quite well to prevent slippage on even the bumpiest of chipseal.
 
Let's see if these photos work...  These feature the new purple bottle cage I got at the HOT rally!  
Let me know if you have any other questions about it!
 
View from the front of the bike (sorry this picture looks like it was taken with a potato...bad focus):

 
View from the side:

 
View from the rear (contrary to this perspective, the bottle cage does not make contact with any part of the frame):