In the last several years, I had a strict limit of one hour a month--and I usually stuck with that limit. Sometimes I would walk back from the Kingdumb Hell and pretend to do street work. Ultimately I totally dogged placing anything.
One time, they made it quite easy. We went to a book store to bug customers (surprisingly, the management didn't kick us out). While everyone else dutifully sought other customers, I sought out areas where there were none. I spent more time browsing through books than I did actually preaching that day.