Premium Themes don't show as theme options using ProSItes

Hi there,
For ProSites, I enabled the Premium Theme option, also, for the "New Blog Templates" Plugin, I enabled the feature "Show templates selection on registration" so that the user can select the theme they want. However, the themes that belongs to Premium Theme are not shown on the sign-up page. Please let me know how to show the Premium Themes on the Signup page so that the users know how appealing are the themes and they can try them and then eventually will purchase them after the trial expires.