I know that folks here often say they hate them, but I have found that I like to wear a little back pack for stuff like that. I have used either the 2.5 ounce sea2summit one or the heavier REI Flash 18 on different tours. I keep them really lightly loaded except for those rare times when I need to load up for a long stretch between restock. If you keep the weight down to just a couple pounds the comfort is fine and if there is a rare day that you need to carry 24 hours worth of water you can cope. At least that is what I have found.

On another note, I am curious about how folks use the tangle bag. It seems like a very limited utility bag to me. Expensive, only 4 liters, and on smaller frames it seems like it would make access to the frame mounted bottles a bit more awkward. The long skinny form factor may lend itself to some particular usage like tent poles or a 4 piece fly rod, but you don't need a $100 bag to strap tent poles or a fly rod to a top tube. Is it mostly for folks just looking to squeeze in that last few liters? I can see that when it is used with limited baggage like just a seat bag and a small bar roll, but I have a hard time seeing much added utility to adding 4 liters when we are talking about bikes with panniers and a rack.