Thank you in advance.
How about an upsell app? KAD Upsell & Cross Sell is a great tool for above mentioned case.
It will allow you to create discounted offers that will be shown to your customers on the fully customizable banner. Products on this baner can be with % discount, free or full price. After offer created it will generate a discount code which name you can change to any necessary one.
You can learn more here https://apps.shopify.com/kad-upsell or by contacting me
Let me know what you think.