I am not 100% sure of this solution but if there was a way for you to have the specific groups as ccaps (custom capabilities) then you could use a conditional to redirect.
I am using a redirect like that based on the ccap (called “element” in my case):
<?php if (current_user_can('access_s2member_ccap_element') && !current_user_can('administrator')){ ?><script type="text/javascript">window.location = 'http://link-to-the-other-page/';</script><?php } else {?><?php } ?>
In order to get the ccap, can you direct the viewer to either different pages for the registration based on their choice, or use different buttons? Would that work for you?