Unless you're using KgPanels for something else, you might try doing this with
Discord Art. The first DART screenshot is a larger (visible) version of Phanx' recommendation, clicking anywhere on the button bar background will not cause the target to change.
Create a DART frame (or more if you have button bars spread apart), make it/them the size and width you want to go behind your buttons and move it/them into place. Set the Alpha to zero so you can't see the frame(s).
It should be that simple.