Not sure if you can do that but you can always add Direct Dial Shortcuts to the home screen. Just press down on the home screen until the pop up appears for adding widgets etc and choose the top option "Shortcuts", Then choose "Direct Dial" then it will show you your list of contacts, Choose one and it will add a small picture of the person (If you have a photo for the contact) and it will have their name underneath. If you click on that it will dial the person straight away.