This may look rubbish but believe me it's not
You will need:
1 peace of tinfoil you could use cellofane tissue or just something squashy.
2 strips of cello-tape.
Wrap the tinfoil around the crayon an fold over the edges
At the top and the bottom wrap cello tape, duck tape or masking tape to secure.
Use the flat side of the pen and you are done.a cheap way to do it