Hi Alex,
So, I opened the /components/com_jfbconnect/controllers/login.php file, went to line 96 and I changed like:
$app = JFactory::getApplication();
$app->enqueueMessage("You must create an account first before you can login with a social network JOOMLEB");
$app->redirect(JRoute::_('index.php?option=com_cck&view=form&layout=edit&type=user&Itemid=0');
// Check if no mapping, and Automatic Registration is set. If so, auto-create the new user.
if (!$jUserId && !JFBCFactory::config()->getSetting('create_new_users'))To be sure of what I done I attach here the modified file for you
login.zip
As guest, when I try to register with Facebook (clicking on the button in SCLogin module) I have back a blank page and in URL:
testDomain.net/index.php?option=com_jfbc...3e1e91696f9cd35cab=1
When I try to do the same with Google+ I have back a blank page and in URL:
testDomain.net/index.php?option=com_jfbc...bOl05ti8ZT3ZLbPGKhwI
Where "test.Domain.net" is the domain where I installed all for tests (You have credentials on it and you can check)
Please, Can you help me to have your Hack running ? 
Forcing Registration and only then Social Connection
