I'm sorry, I simply don't see the need for this. I'm not an auditor but it seems you're attempting to track voucher numbers WHERE NOTHING HAPPENED, As long as you have the A/P account set to not accept manually entered journal entries, your A/P T/B will always match your G/L trial balance. Every entry THAT DID ACTUALLY happen is accounted for. IMHO this is NOT the same thing as auditing missing check numbers or other events that could have a financial impact on the company.
I think you'd be creating a task in the company to track things that didn't happen and that's an effort that doesn't need to happen. Do the auditors track customers that came in the store and then left without purchasing anything? Personally I have enough to do without having to track things that didn't happen and have no relevance to the integrity of the accounting system.