Unfortunately, I think it's not possible to do that in that way. My first thought was to add something like label!='' to choice_filter but we can't filter such dynamic values in the choices sheet.
How about replacing your 5 questions with a repeat group and then build choices based on that group? The form would be similar to the one I attached here: Dynamic choices from repeat - #2 by Grzesiek2010 would that work for you? If so you could for example add constraint
so that the answer can't be empty in a repeat group and your users would just add as many groups as they want for example 2 or 3 not 5 as you have now (the number of question).