Unless I am missing something, there is not a way to send a search to an existing Passage List. One has to save each search as a PL the add them to the desired PL via the ADD menu. Afterward you have to go to delete the ones not desired. 
I am reading a long passage that has two conflicting ideas intermingled through the text. I decided to create a PL of every verse of one idea so I could flow through multiple chapters skipping all content of the second idea. To do this, I searched for key words, saved those verses to a PL and added them to the main PL. What I really want to do is send the searches directly to that PL. 
Maybe there is a better way to get where I am going. Maybe a compound search, adding words as I find them. 
If the Word List comes out soon, maybe I could create  a custom WL and use it as the search criteria, then save as a PL. 
Another thought just came to me. I could work backward. Add the entire passage to the PL and click the (X) to delete irrelevant verses. Thus when done, I could read through chapters of single thought.
Clear as mud?