Discount set by admin

Hi there,

I'm looking for a possibillity to add a fixed amount of discount in admin in OpenCart 2.0.2.0

So when I add a sale in admin, I want to have a possibillity at sales page where I can enter a sum as discount.

The functionality shoud be like
http://www.opencart.com/index.php?route ... _id=14064 (Admin - Free Discount Total Order)

This Extensions only works with OpenCart 1.5.x - otherwise I would buy it.

Thanks in advance!

Matthias aka Pindoyu