There is nothing built in to form wizard to do that for you but it is possible to do it by adding custom javascript to the page. First you would view the source of the html to find the id of the textbox and then you could add javascript to set the value and then clear the value in the onfocus if it still has our default value.
In the new release of mojoPortal we have a new Custom Javascript module that would make it easier to do this becuase it would make it easy to add custom javascript to the page that has form wizard on it.