Isn't it just a matter of going into the UserProfile.ascx file, and changing the dropdownlist code to this:
<asp:DropDownList runat="server" ID="ddlSubscriptions">
<asp:ListItem Text="No subscription" Value="None" />
<asp:ListItem Text="Subscribe to plain-text version"
<asp:ListItem Text="Subscribe to HTML version" Value="Html" Selected="True"
Forgot to add. I can't really test this. I completely removed the profile step from my CreateUserWizard to ensure I can send my new users an Email verification link...