I think the foam is just glued on. You can use a heat gun to warm the glue and make it more easily removed. Then the heat gun can also be used to remove the excess, leftover glue by rolling/rubbing it off while warm. Find some replacement foam, cut to size using the old pieces and use a glue gun to reapply. Take lots of pictures first and as you go to make it go smoothly. You could even use a sharpie to outline the old foam first.
Unfortunately, if any of the IV solution soaked into the fiberboard, You probably can't neutralize it, so you'd have to replace that too. I'd use tempered Masonite. You would also have to remove the top carpet and reattach it to the new piece, along with any other parts.
One thing you might try is to call up a crime scene cleanup business, and ask them if they know what might neutralize the smell. Hey, it's worth a shot, right? Heck, they might even be willing to do it, though I'd have no idea what that would cost.
It might, in the end, just be easier to find a replacement cover from a wrecking yard, depending on how proud they are of it. And, if any of the stuff spilled into the surrounding carpet, you might have to replace that too, plus maybe any padding under it, unless you can clean it sufficiently. Good luck, and let us know how it turns out.
After it's all done, I would install a rubber cargo mat as a preventative measure, such as the Weathertech. I have one, and it saved me when I brought home a leaky gallon of milk with the groceries. In this heat (I'm in Texas) that would not have smelled good, either.
