An app to enable compound discounts

[yaronb]

Hi, 

I'm looking for an app that will enable me to create multiple discounts variations and offer upsell that isn't usually available at the store, for example:

1. The main product is a necklace with a single pendant
2. I want to offer the purchase of a second and even third pendant for a small edition of $ that will be shipped together
3. the pendant isn't sold separately so there is no such product

The final offer should be something like:

Buy this necklace with a pendant of your choice for X$. Add extra Y$ and we'll add a second pendant for the necklace. Add extra Z$ and we'll add a third one.

Is there an app out there that can handle such things? 

Thanks!