I actually agree with you there, "eye-balling" it is the the simplest and cheapest solution!
I terms of a pre-mixed option, the only advantage I can see with that is if you would be able to bye it on the go at some kiosk, shop or food-stand if you need something to eat. Like bying a sandwich or something. Otherwise, for Jake to ship all that extra water-weight around to the end-user seems watefullm to me, and to counter one of the eco-friendly aspirations of the Jake concept. IMO