Tell Geico that you want them to go after his insurance co for you. Not using Geico for your repairs, but have them go after his insurance co. That'll get you a loaner/rental car at their expense (his ins. co.) They'll rip his insurance co a new A$$ and they won't let up until it's done right. They have lawyers just for this type of circumstance.
I had a lady hit my "hauler" and had Geico go after her Ins co and they gave me options of a rental truck, time lost and all kinds of "perks" for the inconveinence and not "dime one" from my deductable.