ASM Brute Force when app success/fail isn't the first response?

Just to revisit this - I've been looking again at the app that has username on screen 1 and then password on screen 2. Is it possible to persist the username entered on screen 1 and then pass via an iRule to Brute Force so that it can be matched against the password as a pair?

As it stands I've configured screen 1 and screen 2 as separate login pages, but not having username available on screen 2 is proving troublesome for accurate BF detection.