Requires KiKit and is based on code from KiKit
KiKit only allows creating panels of the same design. Creating a panel from multiple boards has too many degrees of freedom to implement in a nice GUI. Hence, for creating such a panel, a scripting attempt is necessary.
This script creates a simple panel of two different designs of identical dimensions placed above each other. With including configuration it adds a rail on top and bottom and includes tabs with mouse bites in between boards and between board and rail.
You will have to adjust the script to your own needs