When you upload the email addresses you can upload the additional information along with the email addresses. For information on uploading Email Addresses along with the replacement variables please see Additional References section below.
When the email invitation is distributed, these variables (i.e. {FIRST_NAME}, {LAST_NAME}, ${1}, ${2}, etc.) are automatically replaced with the appropriate content associated with a particular email address.
Custom Variables can only be accessed with the Corporate and higher licenses.