Can't fill in missing dates on merged table because: "Missing values can only be added for queries with one dimension"

[Lewp]

Is there no way to fill in missing dates on an explore before merging when I want to picot by another dimension after the merge?  I am reporting on a metric that can exist on three different tables in looker.  I need to sum all three to get the accurate number and pivot by country.  The issue I am running into is that when I want to only look at countries with low values in this metric data will be skipped because the individual pre-merge queries cannot fill in missing dates when the country field is present.

I have a workaround where I include a country with high amounts of this metric to make sure no dates are missing but I don't like including USA data in a report for Eastern Europe.  I can of course have that USA data in another query and hide all results of it but the more queries are merged the slower the dashboard becomes.

Is there no way around this?  If not I will have to ask for an explore called “Merge Correct” where there is a value of 1 for every date for all of my merges and just hide this in the final merge.  But this feels like something I shouldn’t have to do.