The only option you have not mentioned is to create a place holder record for each time there is no data in order to get the correct spacing. This requires interpolating data from either side of the "gap" in your data.
IF you want more FileMaker Inc. folks to see your feature request you might want to use the Feature Suggestion Form.
I don't think even the Mighty Excel Charting does that, without 'placeholders', does it?
Charting some suspect data from a conversion table stored in an Access database in Excel is where I first encountered that issue and I had to construct an interpolation algorithm that generated the correct data before I could get a meaningful chart in it. That was a few years ago and was using an onld copy of excel for what was available back then so maybe later versions added some options--just like the feature request that we see here is requesting an option. (And it's not the first post to request this capability in charting.)