How do I selectively round UITableViewCell corners?

I'm trying to recreate the feel of the upper part of the iPhone Stocks application. Using cornerRadius I have been able to round all the corners of the UITableView, but when the开发者_JAVA技巧 user drags too far down or up the rectangular edges of the first and last cells show. How can I round only the top or bottom part of the UITableViewCell?