Referring the Affiliate URL to friends

Dear WPMU Team,

I am using the Affiliate plugin and like to send invitation email to a multiple list of emails. I have decided to use this plugin: http://wordpress.org/plugins/invite-friends-to-register

I like to add the Affiliate URL into that plugin but I have no idea how I can find it.

Is there any possibility to access only the Affiliate URL of each user. For example like [affiliate-URL] or similar? Any php code would help too.

Thank you in advance for your support.