When filling in empty cells with placeholders or inserting leader characters between columns, try the REPT function. You simply specify a character or string and the number of times you want it to repeat (up to certain limits for Excel, well into the thousands of characters).
For instance, if you're entering data in the millions of dollars, you might want to fill the empty spaces in your column with hyphens:
This would fill the space neatly, particularly if centered:
But you're not restricted to single characters. Enter whatever string you like into the function in place of the hyphen to get the result you want: