How do I use Marketpress with elegantthemes.com eStore

Hi,
based on your recent blog post about best themes, I went ahead and bought http://www.eleganthemes.com eStore Theme. However, the theme does not work with Marketpress :slight_frown:.
The main issue is that Marketpress Products do not have regular post categories and thus cannot be selected bei Elegantthemes homepage slider option. Is there a way to give marketpress products a standard post category? If so, that would solve the issue (most likely).
I understand that this question goes beyond what WPMUDEV offers as it touches a 3rd party theme, but I hope that you can still help me out.
many thanks!
Boris