Tax on vendor bill discount amounts

Hi

There is a prompt payment discount being entered on the bill payment screen for a vendor.

The amount entered is the total discount which includes a portion of VAT.

How do I split this so a portion of the discount amount is coded to the GL account nominated under the account set under accounting preferences:

while the amount of tax on this is coded to the VAT(or 'GST' as known locally) account?

For example:

The $12,482 is made up of $1,628.20 in VAT/GST and $10,854.66 net of GST/VAT

There is a 3.5% discount applied to the total amount as a prompt payment discount.