UITabBarController's viewControllers and XIB

for a tabBarController based project we populate the viewControllers collection of the tabBar by creating an array of ViewControllers. This creates all the viewControllers at the start [Correct me here if it is wrong]
For my case where the views are created using XIB, I need that when the user selects a tab from the tabBarController then its respective view gets generated and when user switch to a different tab bar, the previous view controller is released. Is it possible?
IN short, I am looking for an alternative way of generating the tabs of tabBarControllers that do not use viewControllers collections
Thanks
Arnieterm