@DC1984, I was able to get this to work. It took some trial and error though.
1. After you have cloned the template, open the line_items_table in Design Manager.
2. In the editor on the right pane, hover over Select column property (Choice) and click Edit. It should be located under Line item column (Field group).
3. This should display the list of fields that you can select in your quote template editor when configuring the line items table.
4. At the bottom of that list, you have the option to Add another choice
5. The property will already need to be created at this time. Just enter the label and the property name.
6. Publish the changes.
This should make the property available when configuring your quote template.
Hope this helps.