Under Downtube Bottle Tips

Having two water bottles in the frame was not a major priority in my last bike purchase, and as a result my bike has the dreaded extra bottle cage under the downtube.

Usually I get by with a bottle in the frame and a second in my jersey, but for longer rides an extra bottle would be really nice. The current cage I have is dropping bottles on the really technical rides I'm doing.

Anyone have tips on the best ways to utilize these bottle mounts rather than leave bottles on the mountains?