In reply to john arran:
How would that work? If the bladder is suspended at the neck of the bottle, wouldn't you end up with the whole bladder slopping about in the outer bottle instead of the liquid? More of a chicken-fillet slap than a splosh I suppose, but still irritating I bet. You could carry the bottle upside down I suppose, but then it would only be a matter of time before it starts to leak.
Maybe you'd be better off with a system of internal baffles in your rigid bottle, like road tankers have to prevent the load from de-stabilising the lorry as it's driven around. Something that can be stuffed into the bottle and taken out again to rinse/wash, like an extremely course sponge perhaps?
Oh, or switch your idea the other way around - store the liquid in the space between the bladder and the outer bottle, and have the air in the bladder itself? Two valves on the lid - one to drink water from, the other to allow the bladder to inflate (and maybe you could also give it a little blow to pressurise the air bag a bit and get a firmer grip on the water).