Addition of multiple (more than two) columns with advanced function

I have a report which is made up of the following columns:

Day consumption | Day Rate | Day Cost | Night Consumption | Night Rate | Night Cost | Total Cost

The day and Night Consumption Columns are Sum aggregations in the master query

The Day and Night Rate columns come from two independent sub queries

The day and Night cost columns are both advanced functions of their corresponding consumption * rate columns.

I need a total cost column which will be day and night cost added together, but I'm unable to do this as the sum function requires it to start with one of the values, which I can't do as they are both advanced functions in themselves.

I have managed to achieve this with making the report a view and then applying the advanced function on those fields, however this solution means that I have had to change my main report data set to enable my required filters to be offered in the child report (this is a separate issue).

I'd rather not have to make the report a view, because as soon as I do that the users are then able to see that view when building a report for themselves, which will just confuse them as our views are documented, and this one will not be (as it's bespoke).

It would seem logical to me that the basic sum and multiplication advanced functions offer more than one other column. Can I do this with my own advanced function?

I've seen this question a few times in the community, it looks like it could be a useful enhancement.

Regards