This is what I would do(I am a bit radical) got that kitty back to your vet! have the surgury ,have him save the obstruction and take it back to the stores vet. You have already bonded to this little guy , you may end up paying for the whole thing but it will be less expensive now (better out come for Dusty too) wait too long he could become a fatal case.
A threat also to go to the paper about store and Vet always gets some kind of action. But I would not leave him at their place they tend to think its theirs still. Had this happen to me once the chain pet store that is now out of business. Good luck. Keep us informed