The easiest way to do this is with a Custom Indicator. Let's take the specific example where we want to put a Moving Average of the Fisher Transform indicator in the same pane as the Fisher Transform. First, create a new Custom Indicator by choosing Setup: Custom Indicator. Then, type in the following syntax: MA(FISH) and click the Save button in the lower right corner of the window. You'll be asked for the Moving Average (MA) preferences and the Fisher Transform (FISH) preferences. Once you've specified the preferences for both indicator, you'll be asked for a name for your custom indicator. Specify a name like "MA_FISH". Now, if you've got the chart open, you can just click the Chart button at the bottom of the Custom Indicator window and the custom indicator should be added directly to the frontmost chart. The custom indicator should be added to it's own pane. Simply drag and drop the indicator into the same pane with the Fisher Transform. The custom indicator may not be drawn with the style, colors, etc, that you would like. Just double-click on the custom indicator and the preferences will appear. Change the style and color to those of your preference and hit OK. The result should be something similar to the chart below.
This process can be used to create the moving average of any technical indicator. More generally, it can be used to create the indicator of any other indicator. Here are a few examples:
The Commodity Channel Index of the Chaikin Money Flow: CCI(CMF)
The Stochastics Slow D of the Money Flow Index: SLOWD(MFI)
The Fisher Transform of the Moving Average Convergence/Divergence: FISH(MACD)
The Rate of Change of the Fisher Transform: ROC(FISH)
Triple Moving Average of the High: MA_A(MA_B(MA_C(HI)))