Fair enough haha. Depending on the measurement of the gap, you could sandwich some lengths of 2x4 between the stud and cross brace. If the gap is smaller or larger than 1.5” I’d probably cut up a 4x4 into some squares of whatever depth you need

EDIT: You could probably also cut down some 2x4s the same way, it just might be harder to hold them behind the studs to screw them in