The absolute best thing to do is draw them out into terrain, such as a forest. If you can move chameleons or skinks into that position, that's optimal. If fanatics hit terrain, they immediarely die.
Barring that plan, the next best thing is use a cheap suicide squad, such as a unit of skinks to move within 8" of them and draw them out.
Barring THAT, there is always the risky way of using a very tough model to draw them out, such as the steggy. I used a treeman once to draw them out. i believe he took 1 wound the entire time. but it's risky because he could roll high and then you'd lose a 300 pt model to 75 pt fanatics.
A few notes about fanatics:
1) Never charge a unit that contains fanatics. Ever. You will take all three fanatiics in the face, and they hurt.
2) Never try to move through them (see #1),.
3) you can shoot them or blast them with magic, but most of the time, I ignore them. They have a very good chance of running BACK into their own unit, causing much harm.