I'd be inclined to add jump-jet MP to the roller-skate MP, but require an additional piloting check, if you get past the initial one. So a roller-Griffin could in theory jet-skate 13 MP (8 run plus 5 for JJs).
(Plus road bonus, where applicable!)
Displace the end-point by the margin of failure in a random direction. Then draw a line between start and end point, and apply terrain interactions in any hex the path goes through. If the path goes through non-flat terrain (rough, woods, etc), then you stop there, and piloting roll to avoid fall.
(Yes, controlled rollering into buildings is a real thing! Don't forget the basement check!)
If the 'Mech collides with something, apply charge damage based on hexes actually moved, not total movement.
(Imagine the scenario. The Roller-Griffin, on a spaceport map, goes for full 14 MP charge - 8 run, 5 JJ, 1 pavement bonus. Makes the initial PSR, then fails the PSR for the jump-boost by a MoF of 3. The end point is displaced 3 hexes - randomly, ahead. The Griffin roller-boosts a total of 17 hexes, right into a LHyd storage farm. Hilarity ensues ...)