I'm looking for a way to keep SKU's when linking between Magento and e-conomic billing system. We have an extension that sends all order data to our finance system (e-conomic) and we need a way to keep the correct SKU's on the products.
i.e. we have medals in gold, silver and bronze. The SKU in e-conomic is 7050G, 7050S and 7050B. To make the shopping easier for our customers we have one product page with 7050 SKU where our customer can choose gold, silver or bronze as an option.
The same goes for our trophies, we have a series with SKU 1870 where the smallest is 1871 and the biggest is 1876. We need to have the correct SKU's without have a products for each size created. Also the stock level is controlled by the e-conomic via an API.
So what I need is the ability to create a SKU's in Magento that aren't products but just to link up via the API to e-conomic. I hope it maskes sense, it's hard to explain. 
The system we use for custom options is Advancaed Customer Option from Mageworx. But they could not help me solve this. So I thought I would ask here if anyone had experience with a task like this?