To stack a key in ECS or EHX, simply double click on the label you want to stack (in the PANELS page) and look in the bottom-right window and see that the ADD LABEL button lights up. Click on a selection from the list on the left hand side of the ECS GUI, of the available resources in the Config, and then click on the ADD LABEL in the right-hand lower box. After you finish stacking all the things you need to stack to that key, you can then rename that individual key with the RENAME button. If you are doing this on a V-series panel, you will see three small white boxes on that label, but they will appear only in the GUI, not on the actual panel.