Hi,
This might be too late but just in case... Yes, I've used it that way in 2 or 3 races last year (2 half ironmans and 1 ironman). It works great. The powder doesn't need much water to form a paste that flows well. I bought a flexible flask (tooth paste tube shape) from Hammer. Very light and flexible with a spout that you bite to suck the paste (no pulling or closing valves).
Hope this helps.
Segundo