discounts and promo codes

I have been looking over the documentation on discounts in version 9.0 and have not been able to figure out if/how you apply a specific promo code to a discount offer.  I know you can use the discounts with the API, but am a little fuzzy on the specifics.

For example, when I set up a promo code now I use offers to apply a specific source code to a specific price type and then use TR_WEB_SOURCE_NO to link the source code with a promo code that goes out on marketing materials.  I would like to know what the steps are to link a promo code to a discount instead of a price type.

Has anyone figured this out yet, or are discounts still too new?

Thanks,

Boann