Flat Taxation (not in percentage)

Thanks Invoiceplane which meet most our needs for our small business, great software.
however I am having some issue while testing this…

I need flat tax amount…for example i am selling a product amounting of 2040 and govt. has implemented flat tax (not in percentage) for the same product, the tax amount is 540, so if i have to calculate the percentage then also i am not getting exact tax value.
Current version is only supported tax value of * percentage of the item value. I will be grateful if you can resolve this issue…Thanks in advance.

Last Update: 14.05.2017

Any idea when it will be resolved?