Are you talking about adding the MACD histogram without the signal line to a chart - as per below?
If so, go to the indicators list on the menu bar (circled at top), select MACD from the Oscillators list, set you fast & slow EMA and ignore the MACD SMA (i.e. the signal line) and go to the colors tab and choose a colour for you histogram (main), and choose none for for signal, and it'll add to the bottom of the chart window as shown above.
If that's not what you mean, can you clarify a little more.
