Very unlikely you can get an American or any large employer to agree personal terms with you, it could open them up to larger liabilities/lawsuits down the line. Most of what you mention is already taken care of in tax-legislation i.e. any part of your package already 'earned' (/contracted for or provided for) will be treated as 'earned' income.
Pay In Lieu Of Notice, PILON, in old days, if NOT provided for in your contract, could have been tax-free but I think/think/think this was closed off some years ago - I stand to be corrected though. If it is in your contract, it will be taxed as normal wages.