You are fighting a losing battle. Don't make your life more complicated than it has to be. The at fault party's insurance company should provide you with a rental car for the entire time it takes for your car to be repaired.
Present - '06 E90 330i sport; Past - '04 E46 ZHP, '00 E46 328i
www.bmwcca.org member #388003 - Use me as a referral & you could win a one day ///M Driving School!!