There is no trick. It just takes a few seconds. But if you remember that you can already block when the animation is still getting up, that might help a bit.
I'm not sure if it helps, but i wait with blocking for maybe two seconds when horse dies. Basicly, falling from the horse, i only press block at the last moment. I don't think it works when you keep blocking pressed when going down. You need to reblock a second or two into the 'getting up' animation.