How to include "NA" option in a slider question

I cannot give you a way to do exactly what you're asking but you could think about the survey flow and include a question first that asks: "which of these did you experience?" then use those choices to determine what sliders are presented to the respondent. Unless you explicitly need to quantify NA responses, the solution I just mentioned works better for the user experience as it can drastically shorten the number of questions a respondent might need to answer.