sounds like a dog just isnt the right therapy animal for your son.
i woulndnt do a hamster, they tend to be nippy and bing noctournal...well...
you might want to try looking into getting a pair of male rats, i know ewwww rats right?! but honeslty they are sweet inteligent and very loving animals who bond well with people, tend to be easy to handle (ive owned many an never been bitten) they tend to be awake when your awake and asleep when your not around to play. getting a pair also means tha ton days hes not up to "snuggling" they have eachother to keep company (rats are HIGHLY social) quiet, soft (look into the rex's) they will learn tricks, easy to keep and not very long lived (5 yrs is old for a ratty)...
but i still think cage wuld have to be in the main house, and hed have to be supervised during an off spell, they are small and delicate afterall, and its highly likly that youll end up being the one doing most of their care...
males are typiclaly much mroe laid back and snuggly than females who prefer to explore...
but they do all love to ride around in sleaves hoods and pockets lol.
however, that being said im not sur an animal might be right for you right now...
instead mabe a comfort item...if he likes the silkies and petting them tends to be calming how about something made with soft feathers that he can carry around...
an mp3 player with a special mix might be good..
whats his take on this, is there something he things would be a big help....
mabe even instaling a punching bag somewhere quiet for during an episode would be helpfull...sometimes you NEED to get it out, having something safe to take it out on can be a help.
i personally keep a small squishy stressball and a small peice of rabbit fur on hide in my pocket for help during anxiety attacks. i find squeezing the ball helps in high tensile situations prior, the softeness of the rabbit fur helps relax and calm after...
you might also be a good candidate for a "therapy fish tank" as i call mine...even a small tank filled with slower swimming but larger bold colored fish, fan tailed goldfish are good for this as are betta fish ect.
ive found for me whenever im feeling high tensile or after a seizure, just sitting and watching my fish swim around is incredibly soothing. again its something youll end up likley being responsible for in terms of water changes and such, but there is a reason many drs offices have fishtanks...roven to lower blood pressure...heck...mabe it would be good for YOU! lol.
i know hes not got the same issues i have, but some of the methods do tend to cross over quite nicely.
in terms of reinbursment for puppy...you might try listing him on hoobly, or mabe the place that helped you get him in the first place could help re-place him