I have prepared a sample example for you, where such functionality is implemented. The example consist of the following steps:
1. Append a second button for the Cars dynamically, when the onEdit event is triggered
2. Subscribe for the click event of both buttons (the original Assign and the Cars)
3. Implement the filter of the Resources data source for each button click, in order to have the different items displayed for the different buttons.
The example is targeting the record "Thomas Hardy". It is not present in the Assign resources, but it is the one for the Cars resources. In your scenario, you will be able to filter the DataSource meaningful and achieve the needed result.
Hope this would help.