Copper pull back

I have a pcb symbol which are fingers only for use on flex tails. Is there a way in the symbol editor of Allegro pcb editor version 17.4 which I can create a copper pull-back constraint or keepout.

We have had failures because sometimes copper from a plane extends to the edge of the fingers and causes shorts.

I would like to have a copper pull-back or keepout 8mils in from the edge of the fingers of this symbol.

Thanks 

HSID