I wouldn't recommend using a pencil, as for the following reasons:
- Tip could be fragile and leave dust & debris in deeper parts of the keyboard
- Could leave marks on the keyboard or keycaps
- Can cause deformation on parts of the keyboard or keycap if used too much force
I don't have a keycap puller either, but I just pull my mechanical keyboard keycaps out with my hand. It should be fine, just pay attention to larger keycaps (spcaebar, enter, etc.) and their stabilizers.
If you have something small enough that's thin, flat, and rigid to stick under the keycap to your assistance,
like the first from the left in this Swiss Knive, you can use them too, just make sure it woun't be too sharp or hard to deform the keycap material when applying force.
Take good care of your keyboard, and cheers.