Bad idea.

1) Frankly a fresh internal auditor is just another junior job, a company is unlikely to make exception if their policy for fresh grad is already 2500. In all honesty, internal audit isn't exactly a powerful or important department.

2)I assume you have verbally informed them that you will be coming down to sign contract. Doing a last minute stunt on the spot will piss off many people big time. They’ll have to engage various stakeholders and relook at internal equity, get approval etc. Even in the unlikely event you pull off, it sets you up for failure because you have offended quite a few people including your boss before you even start work.

Unless you are some hot potato (which I doubt seeing that you are considering joining a normal executive level job), I recommend you not try something like that. Either accept or reject the role upfront.