Hi.

Why not try half and half, chicken and rice mixed with the dry or moistened JWB?
Most people do not want a fussy eater dog but it sounds at the moment that you need to get some nutrition in him - I'm assuming that's why the vet said go onto chicken and rice. So instead of chopping and changing the pup's diet too much, try half and half and then if you want, to you can up the JWB.
Personally I feed wet with mixer when I can't get raw, which my lot much prefer.

Sgurr