Perhaps I misunderstood your issue. You do NOT have to send money when you file Form 4868. Suppose, for example, that you are due a refund, but you just haven't had the time to complete the tax form timely. You can file a Form 4868 to request an extension of time to file. On Form 4868, just indicate the amount you are paying with the extension form as $0. Indeed, the form could list your estimated tax total as well as how much you already paid (e. g., through withholding), and if the amount paid exceeds the amount due, you file the form without sending any payment.
