Just tell the press, “I owe you NOTHING!”
“I will act on my own timetable and your insistence that I provide ‘hot’, ‘warm’, or ‘cold’, assessments of your latest guess is irrelevant!”
He did say a while ago that he’d make an “unconventional endorsement” before the SC primary, so I suppose he felt an obligation to come out with something.
Since I can’t imagine that any candidate would actually adopt a withdrawn candidate’s plan lock, stock, and barrel, I’d say this amounts to a nonendorsement.