It's all practice mate, like all skills. I use my thumb, palm and first finger to blip the throttle, and my middle and third finger to control the brake. You can also change down through the gears at the same time.
It sounds tricky, but it really is practice. Break it down in to seperate functions to practice and then put them together.
I sometimes find flicking the indicators while down changing into a corner and blipping the throttle takes a bit of concentration, but if an old chap like I can manage it. Well anyone can.
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