Shit, I wish I had seen this sooner.
Hutchinson Technical high school on Elmwood Ave near downtown has some ledges and small rails. I haven't been in a while, but there used to be a bowl behind the Tops supermarket on Amherst St - you have to walk down a bike path to get to it. There's also ledges and tables outside of Coca-Cola Field downtown.
You can always stop in at Sunday and the dudes there are sure to let you know good places to go. Friendly people