This doesn't directly answer your question and might not be to your liking, but it's what I do.
Basically, I don't bother trying to keep it cold. However, I do add flavoring. I find that flavoring helps a great deal in making it feel a lot more OK to drink warm liquid. Think of it sortof like tea if that helps. Actually I don't add the flavoring for that purpose, it comes along for the ride.
Most of the the time, and always in warm or hot conditions, I add gatorade powder to the water. When hiking in the desert, it is essential to not only replace water lost, but also electrolytes. Don't mix the gatorade quite full strength, somewhere about 1/2 or 2/3 strength seems to be best.
When you're hiking in the desert, everything gets hot. Trying to fight that will only cost you extra weight and probably won't work for very long anyway. When it's 118°F in the shade, stuff gets hot. It's a lot easier and less stressful to simply accept that. With a gallon of diluted gatorade you can hike around the desert for a few hours at least. Let yourself get used to it, and it's really not uncomfortable at all.
Another advantage of gatorade is that you don't need to eat anything. You're not going to starve in one day, you feel less hungry when its hot, and the gatorade provides some sugar. I usually start hiking in the morning and get back mid to late afternoon. During that time, I only take in the diluted gatorade, then eat something when I get back.