You may be able to take it, however, I wouldn't. If something should happen, you would have voided the rental agreement. Any insurances you would have taken, would also be voided. Further, you personal car insurance, if it covers you, may choose not to since, you guessed it, you vioded the contract by taking the car somewhere that you shouldn't have.

I worked for Hertz many years ago, and have seen this happen before....