AFAIK, there is no other way to do what you are looking for in LN. Programmable dialogs as you rightly said, does not have that capability. I once did play with the standard UI using java script wrapper which used to fiddle with the UI generated by LN which is quite cumbersome and tedious because you have to go through the source, find the elements to handle and play with them using DOM. But well, worked for me. I will be pleased to know if there is any alternatives.
Unless you try to do something beyond what you have already mastered, you will never grow!