Thank you for your answers. Here is an update.
To make a bubble flare by using a double flare tool plus deleting the last operation is not cutting corners. Actually it say so in the users manual for my inverted flare tool. I discovered it when I read it once more.
The kit car / hot rod guys using Jaguar rear axles do it all the time, because the Jaguar rear brake calipers uses this flare type.
But buying hardlines with bubble flare in one end, cut the line to correct length and then make the last bubble flare myself is also a good idea, of course.