You could make a narrow floating text box or one-column table, set the font to the same as the body text & type in a number for each line. Then move it to the location you want. To have this repeat on each page, move it to the section master. This will only work if your line spacing is the same as the body & vice versa. If you have any space after a paragraph that is different that the size of a full line, the numbers won't line up.