Can I strip a neutral wire and use it to pigtail ground wires?
Yes, as long as they are thick enough (thicker is always OK) and you must strip the whole wire because grounds must be green or bare, not white or any other color. If you are concerned about the ground wires shorting against screws, put tape over the screws, not over the ground wires.

From Grounding Conductors size (PDFP:

For 15A - 30A, the sizes are the same as the hot &amp; neutral for the same size circuits:


15A - 14 AWG
20A - 12 AWG
30A - 10 AWG


Above 30A, you get to downsize:


40A - 10 AWG
50A - 10 AWG
60A - 10 AWG
100A - 8 AWG
200A - 6 AWG