If I understand you right, you want to redeem eg. on QF but don't have enough Avios, so once you know the flight you want is available for redemption, you plan to transfer Avios from BA to AY?

If I understood you right, what you could do is first do everything regarding the transfer except click the final OK. Then call AY and book your award, and once Janica tells you the flight is available but you don't have enough points, you just click "OK". The points post instantly.