Custom indicator

I want to know how to add EMA in Elder Force Index indicator in Pi??

I checked a blog and Mr. Kamath said custom indicator can only be added through backend.

If this is the case, add this in backend as I wish to use EMA in Elder Force index.
 

Force Index(1) = {Close (current period)  -  Close (prior period)} x Volume
Force Index(13) = 13-period EMA of Force Index(1)

you can apply the above indicators to a chart and save the chart as template and then you can use these template with your custom indicator for all the other charts. by applying the template saved.