I put tracts up on public bulletin boards at work. These boards hosted all type of employee to employee communications (items for sale, event announcements, requests for ride-sharing, etc). I did this until work management dictated that only work-related notices be posted.
My thinking is that you run the risk of offending a customer, who will then complain to management. You probably know better than I what management's response will be. If you think that they might fire you, you might do well to find another distribution avenue.
I also placed tracts on public bulletin boards at nearby public universities. Something else you could do is to include a tract with any mailings ... say to pay bills, etc. I've always chosen to have my checks printed with a helpful bible verse. I've also mailed tracts to households within various local neighborhoods.