My far better option at the time was this. Operate the second part of the economy cabin not as Qantas but as a low cost section. Call it Qantas light if you wish.
Reduced seat pitch, no IFE, no free baggage, restricted carry on, no seat selection, no access to Qantas Club, no international connections, no free meals/drinks, no pillows/vlankets no QF FF points. Call it "second class" not economy so that business travelers (under most work agreements) would be unable to book it.
That was tried before during the Ansett/Australian/Compass war days and was a dismal failure, remember "discount economy" by AN and TN. Way too confusing for both staff and customers and led to much angst for all. It did not last very long.