Make sure you are displaying the level strip alongside the x-sheet.
Open the configuration for the keyboard shortcuts, and assign a key to "Duplicate Drawing" in the Menu Commands-->Cells-->Duplicate Drawing (highlight the entry, and hit a key - I assigned it to the numpad * key).
Select an empty frame in an empty x-sheet column. Start your drawing. Then select the drawing in the level strip. Hit the Duplicate Drawing shortcut key, and use the cursor arrow key down to ensure you are working in the duplicate. Draw. Duplicate, arrow down. Draw. Duplicate, arrow dawn. Draw - ad infinitum, When you are done, select all the frames (or just a selection), and expose them in the x-sheet.