Have you tried folding up a flat nappy into a pad and putting it where he needs a little more absorbancy? It would add a little bulk but hopefully not too much. Also have you tried soaking the nappies in a bit of vinegar (with cold water rinse) before washing? It gets rid of the urine/faeces which bonds to the soap residue. You need to use quite a lot of vinegar the first time you do it, I used about half a bottle of distilled white vinegar.