There is currently no automatic system to set this up, and you need to manually implement this.
- Add the data in the feed using custom meta fields
You can also use https://apps.shopify.com/multiple-google-shopping-feeds
Which allows you to map metafields as well. And also the cost of goods attribute. Which might be a bit simpler then the Google and Youtube app in terms of setup (assuming you have added the auto_pricing_min_price attribute, you could also set up a percent of price for this attribute, so no extra metafields are needed).
- Update your checkout to accept automated discounts (contact a shopify developer)