How to create a relationship between two connected dataset tables?

So far as I know there's been no movement on the feature request and use of formulas will still not work, so the only solution is to modify the source data to include a unique value that exists in both sets.
The easiest way I found to do this is to manually concatenate multiple fields together. You can do this manually in excel, but for automation purposes you'll probably want to make a script and set it to run automatically using windows task scheduler.