I can't hold it for 500 miles. Can you?
Why does a car need to go more than 100 miles on a charge?
If you are doing cross-country driving, then you can hitch an APU and gas tank to your electric auto which would magically turn it into a hybrid.
You could rent the APU or you could buy one for 2-5k depending on the fuel source (deisel, Ethanol, Kerosine, etc...)