Google has a newish program that's free to add to your shopping ads called Google Merchant Promotions. It allows you to add specific or general promos to your ads.
"Merchant Promotions is a free feature that allows you to distribute online promotions with Shopping ads on Google.com. When you add promotions to products that you sell on Google, shoppers see a â€œspecial offerâ€ link (e.g. 15% off, free shipping, etc.). This link can increase the appeal of your Shopping ads and encourage shoppers to buy."
You can set up a feed to add these. I'd like to add a feed that would find and upload my sale items and/or work with CS Cart Promos.
There's a doc here as well:
Has anyone set this up? I'm looking for some examples of feeds, or an add-on that would work with it.