Joomla Extension Customization

I am working with the News Show Pro GK5 extension by GavickPro which allows for the display of Joomla articles, K2 articles, or products in Virtuemart. I would like to have this module customized in that the virtuemart categories are displayed only. An example of the output can be seen at www.lifesongcompositions.com. It is the module on the bottom with the six images being displayed (currently linked to Joomla articles). In the admin section of the module, there is a drop down menu where the user can select Virtuemart categories. I would like to use this option to display the categories only option. Typically, this will display products in the selected categories. The user will also receive an error when they elect this option which states “specific data source is not supported by selected Portal Mode. Please change the data source or portal mode”. I would like to use this option in any module mode (under basic settings), primarily for the News Gallery mode. 
Any questions, please let me know. Thank you for your interest.