One solution would be to create your own subclass of the TabBar or just create a generic UIView that has the same properties as a TabBar (e.g. array of buttons that get displayed inside the view at certain heights, with the center one with a different height or offset value).
Another route you could take is to search and find other frameworks that are out there to use that do the same sort of functionality. A quick search on cocoacontrols came up with a couple options, the one that looked closest to what you are looking for is the RaisedCenterTabBar.
