I was at SPN Con in NJ this weekend, and I did get to ask Misha the vital question -- Did he give any consideration to Cas' transportation and whether or not he was reeking of fish for the whole episode? He told me yes, but that Cas had also thrown up blood all over himself, so that he smelled like vomit, blood, and then fish, and that swirl of odor was repulsing people. He also admitted the possibility of the hospital laundering the trench and suit while he slept. (When he said this, Misha forgot the word for sleep and the audience had to help him out. It was completely adorable.)

Anyways, I found your answer (sort of) and have to tell you again how awesome you are for bringing this up! I hope you don't mind I borrowed it for the Con. It was too awesome not to ask. It's fabulous!