I think the way apple has done this is probably the best solution, where you can change sensitivity by moving your finger away from the slider.
This is something I intend to add soon.
Regarding the +/- buttons on the iPad, I kind of regret adding them the way they are now.
May be a good idea to send arrow command like 6233638 suggested, but not sure if that would work in all instances.
Could also make the skip value a setting.