This is an advanced tutorial that explains how to automatically enroll a member in your loyalty program if they try to get points and they're not currently a member.  In order to set this up you will need to contact your system admin.

You will need to create a new wi_get entry for the reference_type of customer-nonloyalty with reference_no 0 allowing you to process all new customers added.  You can then assign the item_type as membership and item_no as the membership_no you want them to enroll in.