i don't think the indexes needed for a relationship work are accessible in find mode so this technique might not work.
Guessing here of course.
I'm confused just reading it.
A dwindling value list is used during data entry so that a user can't select the same value twice. But that typically means that you have a set of records that are used to produce an "exclude list" to keep the user from making a wrong selection from the list. What defines that set of records can be very different from one application of this technique to another.
But you want this in find mode. What defines that list of values that then exclude values from your list? Would these actually be other requests in the same find that they are setting up or some set of records that controls what they can't choose anymore for this find?
I do this with Global fields set to the value-lists. And do the selection(s) from Browse mode. Then if you need other fields to "find", you can take the selections to variables to use as the criteria in a scripted Find.