If I am understanding you correctly, you would like each paragraph (or is it sentence) to begin at the left margin, with a blank line between each.
If this is so, I believe Calibre can accomodate this.
I know I change everyone of my ebooks to Left-Justify (my preference) with an indent for the paragraph. But Calibre can change it to Left or Full Justify and can, I believe, add or remove lines between paragraphs.
If you mean each sentence begins at the left margin, I'm not sure Calibre can do this automatically.
You could post a question in the Calibre forum.
Good luck to you.