I don't believe there is a method in place to pass a "newly installed" flag on an apps first install by a user from an invite instance. I haven't tried this out myself but I believe several developers have used a custom yml:message e-mail to forward a user to the app page with a query string param at the end to read in - that param would be the guid of the user who invited them. Something like that may work in this instance.
Jonathan LeBlanc Senior Software Engineer Yahoo! Developer Network Twitter: jcleblanc