Hey... I've been in that boat.
Several years ago a friend tossed his cookies in the floorpan in the backseat. He'd been drinking a lot too, so it filled it up quite nicely.
He was too drunk to clean it the night it happened, and the next day he claimed he just couldn't do it or he'd get sick again.
I was working two jobs at the time, so I had to work all afternoon, then drive straight over to my other job and work all night.
I didn't get to start until about 10:30PM... after it had baked an entire summer day under the heat of an Alabama sun.
My advice is to just muscle through it... Throw open all the doors and let it vent for a few minutes, and then just attack it and try not to think too much about. Just get one of those cheap little mini-whisk/dustpan deals and a few rolls of paper towels and just scoop and toss and wipe. Or, if you've got access to a wet/dry vac get the bulk of it up with that.
Once you've got the bulk of it out, hit it several times with some soapy water to dilute it and just keep sucking it out.
Then shampoo it or whatever and or take it and let someone else shampoo it. Bill your friend for it if he'll pony up.
Me, I did it all by myself while that bast**d stood there going "I'm sorry man, I'm really sorry... I'd help you if I could."
Whatever... builds character.