Advance Pricing discounts header level

Hi ,

We have the below requirement , please let us know incase it is possible to achieve this header level discounting .

1) A header level discount is needed which will allow user to enter specific amount(dollar amount) . For example we want to deduct  100$ from then header price of sales order .

As of now we can see only percentage discount at header level. Like 5 % 10% etc .

2) A promotional discount is needed . For eg : If a sales order crosses 5000$ amount then a item like "AS54999" should be free .

Thanks