I stand to be corrected of course if anyone does have first-hand knowledge... but I’m pretty certain this isn’t possible. BA Holidays products are managed not only by a separate team, but also in a different system. The flight only exists in the corresponding BA system as long as it’s attached to a holiday product, so if you cancel the holiday, it would cancel the flight. In addition, BA revenue management have very strict rules against tour operator fares being used for non-tour products, so if they got you a discounted flight (which admittedly you wouldn’t know) then it can’t be used without a holiday product - this goes for external travel agents as much as the internal one. You could of course rebook flight-only at the prevailing rate to get the additional flexibility in any case.