It is important to keep in mind that eBay has very strict policies against duplicate listings. We don't support creating multiple listings from a simple product in Magento. What is possible though is to create a variation listing from a Configurable product in Magento. In addition it is possible to create specific listings from one or more of the Simple products associated with the Configurable.

By default the Simple - Associated products are not shown in the eBay | Codisto > XpressGrid. 

Displaying Simple - Associated products

1. Click on the Column Settings button

2. Tick the Type column to display it in the XpressGrid

3. Click the filter icon in the header of the Type column

4. Tick "Simple - Associated" to show Simple products associated with Configurable products in the XpressGrid

Listing "Simple - Associated" products

Now that the Simple products associated with Configurable products are visible in the XpressGrid, you can list them the same way as usual.