Bit of a weird combination. Hydration packs are usually used for trekking, climbing, skiing etc something I wouldn't have thought you'd take a laptop with you.
Oh-well.
Is it the Camelpak brand you want specifically? Or with any other brand of hydration pack suffice?
Usually Camelpaks are relatively small but I know for a fact Dakine produce rucksacks with a hydration bladder inside which should fit a 13''-15'' MBP in, maybe a 17''.
Plus, being rucksacks I would imagine there was some sort of waterproof barrier between the compartment and the water bladder.