Additional fields in Subcontract Invoice Line items to record amount claimed by Subcontractor

When entering a Subcontract Invoice, to meet the legislative requirements in Australia (which I believe is also needed for the UK), two additional fields are required in the Line entries section as shown in the file attached.

The two fields needed are:

A: Subcontractor Claimed Amount: Amount entered here is to exclude Tax

B: Comment: when the "Subcontractor claimed amount" is different to amount under "Current Work" then a comment is to be entered to explain the reason for the difference. Generally amount under "Current Work" will be lesser or equal to the amount under "Subcontractor claimed amount".