Yes, Cruz has indeed put himself in a box, but if he has to choose between endorsing Trump and disappointing his #neverTrump kook supporters like Beck, Krystol or Romney, vs. not endorsing Trump and turning off everyone else, well then.... I know what I would do!
Maybe Cruz could endorse straight out of the gate, and then utilize some form of the very good suggestions you made, to ease the shock and disappointment of his most anti-Trump supporters. Some eloquent warnings about the calamity that would be a Queen Hillary reign could make that bitter medicine more appealing.