there are a variety of pouches you could get that'll fit over the webbing and padding of your waist belt, i've carried water in this way in the past and it works very well. or maybe you could modify the straps of whatever pouches you've already got to fit over it. the other option that springs to mind straight away is to use the low-carry british military pouches that someone else already suggested, i've used these too but don't personally like them because they hang too far down my legs for my comfort but that's just a personal thing, i know it works fine for other people. other suggestions would be to put things in pockets or around your neck, this is what works for me but obvioulsy it's limited by the size of things you want to carry.
hope you find something that works for you.

take it easy,
stuart.