The \` command allows you to put text flushed right against any tab
  stop, including tab stop 0.  However, it can't move text to the right
  of the last column because there's no tab stop there.  The \` command
  moves all the text that follows it, up to the \\ or \end{tabbing}
  command that ends the line, to the right margin of the tabbing
  environment.  There must be no \> or \' command between the \` and
  the command that ends the line.