If he really wants her to shift, she will, but given her strength and flexibility, this is easiest for her. She'll lock her legs around him at the ankles and hold on tight.

The slow rise from the ground elicits a small gasp from the rogue, but only in the best way. Once they get high enough that she can no longer make out the faces of everyone on the ground, she laughs. Not at Bill, not at the sight of the small people below them. No, she laughs from the happiness this sort of thing brings. Were anyone to ever offer her a super power, she would ask for flight (once the concept of a super power had been explained, of course). For now, she's going to hold tight and enjoy the ride.