Actual you assign lifesize:firstname.lastname@example.org to the lifesize app by default. It would be great if you also assign sip:xyz.yyy to open lifesize app on client.
May you also add a link sip:email@example.com to the invitation mail (from app and outlook-addin) - with this option it is possible to join the meeting just clicking on that address.
If you click on the link on the web-page (lifesize:firstname.lastname@example.org) the lifesize app client app window is not opened automatically if it is opened in background also the system joins the meeting.
May the user information in the app could be sip:email@example.com.