No, this is not possible. The counter systems automatically pre-auth your credit card based upon whatever policies are in place by the rental company. For most, that means a pre-auth amount equivalent to the total cost of the rental plus a deposit (usually $150-$200), but some companies will not take an additional deposit and just auth the rental amount. The counter reps have zero control over this. It's all handled automatically by the computer system. You will need to ensure you have enough credit on your card for the pre-auth or you may not be able to rent at all.