You'd have to already killed, dismembered, and carefully packed someone in there to be able to close the space up. I think not.

The reality is the space really isn't that closed-up. For normal boats, these rooms aren't hermetically sealed. You really are trying to quell the fire so you can figure-out what was the cause and really remove it. The supression system will neither cure the problem nor will it likely completely put-out the fire.