Format both columns as "0;-0;;@"
You can enter 0's, but they aren't displayed.
NB! the value of cell with entered 0 in it remains 0, Formatting cant change the value in cell (date format will be exception, as with it whenever the entered value can be interpreted as date, the Excel itself takes over and replaces the entry with date in current format) - it only affects how this value will be displayed!