Xlab's Torpedo Mount allows you to place a bottle and cage horizontally between your aero bars. This reduces the front area of the bottle by 68%, giving you appreciably less drag than upright bottles. Four straps with silicone grips hold the Torpedo in place and provide full adjustability. And, the Torpedo fits aero bars from 9 to 14cm apart and requires no tools for installation/removal.
Intro: XLAB Torpedo System - Horizontal Aerobar Hydration Carrier