Ha! I'd be curious to see this theory put into practice.
If you're using a bladder, having the water inside the bladder freeze solid is less of a concern than the hose and valve, which would easily freeze even if you had hot tub jets inside the bladder. I've used a tubeless MSR bladder in the past, but without insulation the water inside freezes fast and the jostling of water inside the bladder causes ice to form on the lid threading and can be almost impossible to open. If you really don't water on your back I think the best strategy is to buy 1-2 Hydroflask bottles, which I've had luck with keeping water slushy but drinkable for upwards of 12 hours in below zero temps (by combining with an OR insulation sleeve). They don't fit as well inside a frame bag, but bladders are pretty much useless unless they're on your body.
