Sorry but no there is nothing built into mojoPortal to support that. Possibly you could do it by implementing your own custom registration page and adding a login control
<mp:Login ID="login1" runat="server" SetRedirectUrl="false" />
There are Web.config settings that allow you to point the register link to a custom page, or you could implement your own link and put it in layout.master file of the skin removing our login and register links.
Hope that helps,
Joe