Stone lifts Prompto up, cradling him between his palm and his chest like he's holding a cat or some sort of small rodent, nudging at his elbow with a thumb to get his hands on the raised scales along the ridge of his collar to hold onto. They actually make extremely convenient hand-holds.

Only once he's sure Prompto has a good grip does he crouch down further, spread his wings, and leap up into the air. It's a bit of a stomach-lurching experience, but if Prompto likes those sorts of things, he might enjoy it.