How can I apply different discount rates to each product size?

[linens247]

Greetings, I am looking to apply a different discount rate to each size of a particular product. Shopify only allows a flat discount, % off, and BOGOs across the board. Is there a way to set the MSRP and discount associated with each individual SKU (with a code)? Is my only option to build duplicate products by size and apply discount codes to each?