Photo credits go to Matthias Ries
Via mocoloco comes this water bottle holder concept for your whip by designer Matthias Ries. While the concept may look good at first glance, it appears that the bottle would have to be unscrewed from the plastic fitting anytime you'd like to take a sip.
It's also unclear how durable the plastic threads in the fitting are, and how much weight they could support. I suppose once your done with the bottle you could always hack your own fender out of it. The idea is interesting because in theory it could fit lots of different kinds of bottles and hold them somewhat securely. Matthias's website states:
Bottleclip is designed as a cheap bottleholder or advertising gift that simply snaps onto any standard sized mens bicycle. Due to a normed thread most bottles can be screwed directly into the clip. The target group is certainly not sportive cyclists but rather touring seniors or families that would like to have an extra liter or two easy at hand.
While it may not be the easiest to use quickly, it could provide a good way to carry a refill for your main bottle in style.