Unless QF make allowances for travel (breaching the T&C of QFF) in a the period prior to membership you cannot claim milage & status for flights prior to being a member.

Has anyone had any experience with this?

http://www.qantas.com.au/fflyer/dyn/program/terms

9.1.2 Points can only be earned in relation to acquiring goods or services or other transactions made by the Member after the Member's enrolment date.