Hey neilfein, I have a 900mi ride coming up at the end of the month and I'm doing the same thing...looking for places to put water bottles on the outside of my bags or frame. I had some braze-ons installed on the down tube of my '88 Rockhopper Comp for my fuel cell, but that's a pretty common place for cages on touring bikes.
If I come up with something cool, I'll send you some pics. Like you, I'm going to want to reclaim some of the space in my bags.
Jerry H