I'm afraid the chart doesn't provide a separate style for the interpolated parts of the series.
This will have to be a separate series that only covers the gaps. Probably not that easy to do.
Another problem is that dash type can't be set right now.
This is something that we can address sooner than later as all the pieces are in place for it.
Please, file a request for these features on our UserVoice portal
if you have minute.
This will help us gauge the overall interest and prioritize.
Apologies for the caused inconvenience.
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