Don’t be silly. How could Trump get Rubio approved for the court after he destroyed Cruz’ credibility? It would never happen.
I think you are mis-reading the idea: Trump should promise to nominate Cruz for the Supreme Court to consolidate Cruz supporters behind Trump (if Cruz cannot pass Trump in the votes) but leave Rubio following orders back in the Senate. Rubio has too little experience to justify a SC nomination anyway. That wouldn't stop a democrat with equal experience, but the rules are different for a democrat. (If you are a democrat, there are no rules today>)