I think that if Portland traded for Miles at this point, only for the purpose of refusing to allow him to enter games, his agent would immediately file a union grievance for interfering with his livelihood and affecting his future earning capacity. The league would also have the ability to step, as it has the authority to prevent any team from circumventing the salary cap or the intent of the CBA; this scenario would seem to fit under that category. I also think that it would damage the reputation around the league of both the Celtics and the Blazers.
Theoretically, it's possible, but I think it's very doubtful.