Hide series, keep trend line, but both also in legend

Hello. I have a Line chart with multiple data series each with its own trend line.
But I want only trend lines.
I know how to hide data series lines from chart, I just select Line style -none- and it is hidden.
But now I want to do the same in Legend. I want a legend for trend line, but I still have a legend entry both for Data series and for Trend line.
If I change properties of Data series to “Hide legend entry” then legend entries both for Data Series and Trend Line disappears.

Is there some way how to hide Data series from chart and legend, but keep Trend Line both in Chart and Legend (beside calculating trend line values manually as a separate Data Series)?

Thanks for help.