I am thinking there isn't much on the floor of the car that would be likely damaged by the coolant. Could you rent a machine designed for carpet and upholstery cleaning, which basically pumps liquid onto the carpet and then vacuums it up (wet vacuum)? I've used one which has a hose attachment to clean very dirty carpets in my home. Maybe do the wetting/cleaning multiple times with clear water. You would have to leave the car open and/or use a fan to dry it out, but the vacuum might get nearly all of it. Is your climate warm now?

Another option would be some absorbent granules like cat litter or things used to clean up spills in labs and factories (sweeping compounds). You'd have to have a good dry vaccum to get them up once they did their work.