Out of the box, drag-and-drop ranking does not support having different respondents rank different numbers of items. I do have some custom code that might be useful for your situation, however.
"Ranged Drag-and-Drop Ranking" allows respondents to rank different numbers of items. You could use this to allow respondents to rank between 0 and N items, and then label the left container as "do not use product":
http://sawtoothsoftware.com/community-question-library/1751-ranged-drag-and-drop-ranking
Alternatively, you could use "Categorization" to create a ranking question with three containers. You could have an unranked container, a ranked container, and a do-not-know container, then require that every item be ranked in either of the two latter containers:
http://sawtoothsoftware.com/community-question-library/1736-categorization