Troubled mind:
"I noticed the Witnesses put up a table at our local Wal-mart last summer ,and i have been thinking of asking the manager about putting up a cult awareness table too ! Let me know if you go through with it ...."
Troubled one; all you have to do is to wait and see if the Witnesses are there. You don't really have to ask the Manager but it would be nice to inform him that you plan to be there and why. When you explain the 'why' part, you might actually get support from management.
I suggest emphasizing their totalitarian nature by using the worse example of disfellowshipping; that of the victims of sexual molestation.