andres_Santiago,
Our Request feature can be added to any page you want, however you want. Wherever the user is redirected after they register with JomSocial, you can easily add the JFBCRequest module or the {JFBCRequest request_id=XX} tag with some text asking the user to invite their friends.
There isn't a way to force the user to send any invitations, but it doesn't sound like that's what you're looking for anyways.
Let me know if that helps explain or if you need more information.
Thanks,
Alex