I think GIB North has an absolutely routine 2♠ rebid here. Incidentally, one South rebid 1NT and did indeed get 2♠ from his partner. I would think 3♠ is, if anything, better over 1NT than over 2♣, though still bad.
Of course, if GIB played WJS, rather than these weird Soloway Jump Shifts which never come up and noone understands, then this would be even easier.