that is one of the downfalls to the micro-packs that are out there. You want the SUL weight and the fact that they are inexpensive is a real bonus, but how do you haul water? And water is one of the heaviest things, especially on a day hike.
With the really small packs without a waist belt, a waist/fanny pack comes to mind, but by the time you add the waist pack, you might as well have a larger heavier pack that has the bottle pockets. It would work though, and the weight would be distributed to your hips. You could rig up something more elemental to wear around the waist that is simple loops or bags to hold bottles. Lowepro (the camera bag maker) has a mesh bottle holder with a belt loop. Nalgene and MSR have made them too.
Another solution is to use a sling for your water bottle, carried cross-body "baldric" style. It is easy enough to create your own, and there are all kinds of them out there to purchase. Bear Grylls carried a Pattern 58 NATO water bottle through a couple seasons with a simple paracord sling. Using some 1/2" webbing would make it a little more comfortable. I once made one from a sling of webbing and a couple rubber ands cut from an inner tube.. Chico Bag has a nice take on it: http://www.chicobag.com/p-53-chicobag-bottle-sling-repete.aspx.
I have an "H2O to Go" brand rig that is a mesh bag with a drawstring top and has 1" webbing sewn down the sides and under. It came with a tall (13") PET water bottle and the whole thing weighs 3.5oz. If you can sew a stuff sack, you could whip this out in a few minutes.