Dynamic Pricing and in-app purchases

My app is essentially a digital marketplace where users can set their prices and sell digital products to other users. I read the App Review policy and found out that I had to implement in-app purchases if I wanted to sell digital products on iOS. In the process of figuring out how this was going to be implemented, I realized that in-app purchase items have to be created ahead of time. This means dynamic pricing is not possible, so what do now? Is there not a way to programmatically create in-app purchases? If there is not a way to do this, and I cant use my own payment processor, what is the way forward?