I have been trying to implement StackView Widget and ListView Widget as a seperate jar. If you know some java (or are willing to learn, like I had to) you could make something from attached files.
It's not the best way of doing this, but I didn't want to spend time on learing java since this is just a hobby for me. Knowledge of C and b4A is enough for me.
I have attached a sample b4A project which I was using for learing/testing. To compile it, you have to copy ListWidget.jar into your additional libraries folder.
I have also attached an eclipse project where you can modify the widget layout (widget_item.xml, widget_provider_layout.xml, widget_provider.xml) and java files. If you make any changes to xml files you have to copy them into \resources directory in b4A project.
Have a look first if this is something what you would like to do. If yes, then maybe I can help you, with my limited knowledge of java. Or maybe someone else will make something better.