We were discussing this in another forum and I think I said I doubt there was anybody providing this service - well I was wrong. 
This is not a recommendation underwritten by AIG - didn't they go bust : ) but it proves that it is possible to get this type of car hire excess insurance from somebody other than the rental company
Car Rental Excess Insurance - trusted Global Car Rental Excess Insurance - Excess Insurance
This is not a recommendation underwritten by AIG - didn't they go bust : ) but it proves that it is possible to get this type of car hire excess insurance from somebody other than the rental companyCar Rental Excess Insurance - trusted Global Car Rental Excess Insurance - Excess Insurance