I use piper’s grip on my right
hand–this facilitates slides,
cause you basically straighen
the finger, sliding it over
the edge of the hole.
But how do you do it
on the left hand holes?
Well, in my case I use piper’s style fingering on both hands, so the same way… 
I don’t use the piper’s grip with my left hand (hard to use the keys otherwise), and I cover the holes with the pads -not tips- of the fingers. Slides are more tricky but doable.
I don’t always straighten the finger, tho this can be done. In my case it can often depend on the tune as certain approaches are more effective at different times.
Other ways that I use: pull my finger (not THAT!) back, sliding it off the tonehole; another that I’ll use sometimes is to roll the finger sideways off the hole, and this can be done in either direction.
Come to think of it, I use these approaches with both hands! Hope this helps.
N, sliding away
On my left hand I use:
Index Finger second joint
Middle Finger second joint
Ring Finger first joint pad
On my right hand I use:
Index Finger second joint
Middle Finger second joint
Ring Finger second joint
-Aaron