He should just simply ignore it. It was never law. Prosecutorial discretion has always been up to the reigning power. Simply issue an executive order that all immigration violations will be prosecuted.
I don’t understand that since an EO only operates what is within the Ex Branch, then the SC is crossing out of bounds from its Judicial Branch to another Branch in attempting a ruling on Ex Branch internals (EOs) - therefore violating that separation of govt. powers thingy.. :(