how to use line tool only one frame

The line tool in my video for example is used as a guide to correct the lower arm movement of a character. On the top layer  frame is the line tool and on the bottom layer frame  is the character and as the artist draws the line on "one frame" the line tool is one drawing and appears the artist is drawing different lines on character arm to use as a guide to fix the arm movement but the lines connect and appears to be one line drawing   . When I try to duplicate the line tool guide it creates separate lines that are not connected and when i play the animation it plays as separate lines not one unison line guide  . I hope I'm making sense .