Improving dynamic list selection

I have the problem related in this link for a desktop app:

Suggestion for list selection and populating related lists dynamically

but instead of 3 list I have 7 and some lists have more than 20 items to choose. I like the idea of showing the next list only after a item is selected. The problem that I have is the layout. It takes too much horizontal space if more than 4 items are selected. Is there any other way to organize this? I don't like a lot the accordion solution, because only two first selections are required and I have to create accordion options dynamically. It isn't a web app and interface components are hard to code.