Advance Pricing discount at order level

Hi,

I am using Advance pricing for base price not P4106.

I have two adjustment defination

     -Base price

     - Discount based on customer and item group.

Now i want to give order level discount which will be applied at order level.

Lets say - Base price - 100 USD , discount is 10% line level

5 lines in Sales order

Additinal 5% discount should be applied to complete order total value. how this can be set if yes do i need to add new line. can it be done without additing new line.

Regards,

Abhijit Joshi