Just pick up a hammer and smash a fingernail or two before you pick up your guitar.. Garantee you'll make some good faces for a week or two.. Well you at it make sure you do both hands. Do your picking hand thumbnail. A couple cactus thorns work good..
Before a performance wipe your brow with a damp salty rag so when the sweat runs in your eyes you'll enhance your already excruciating pain.
A tack in a shoe.
Bengay in your skivvies..
Break out a tooth filling and stuff you cheek with sugar.
And have your women or man in the front row getting it on with worst enemy..